Attempt to approach the role of phenolic phenylpropenol structures in the photoyellowing of softwood mechanical pulps

Article abstract of DOI:10.1139/v02-123

Three biphenyl (I, II, III) compounds and a benzylarylether (IV) compound were synthesized to detect and quantify the presence of phenolic phenylpropenols in unbleached, peroxide-bleached, or sodium borohydride-reduced mechanical softwood pulps. The methodology used is based on a gas chromatography - mass spectrometry search of the prepared compounds in the residue obtained after ethylation, thioacidolysis, and desulfurization of the pulps. Detection of biphenyl I (≈4 × 10^-6 mol g^-1) in unbleached and NaBH₄-reduced pulps is indicative of the presence of phenolic coniferaldehyde units in these pulps. Traces of biphenyl II, found in the peroxide-bleached pulp, probably came from ferulic acid units formed by oxidation of coniferaldehyde by H₂O₂. No biphenyl ether III or benzylaryl ether IV were detected in the three pulps. This result indicates that phenolic phenylpropenol units are not present in softwood mechanical pulps and do not contribute to the fast part of their photoyellowing.

Full text of DOI:10.1139/v02-123

1223
Attempt to approach the role of phenolic
phenylpropenol structures in the photoyellowing
of softwood mechanical pulps
Brigitte Ruffin, Stéphane Grelier, Aziz Nourmamode, and Alain Castellan
Abstract: Three biphenyl (I, II, III) compounds and a benzylarylether (IV) compound were synthesized to detect and
quantify the presence of phenolic phenylpropenols in unbleached, peroxide-bleached, or sodium borohydride-reduced
mechanical softwood pulps. The methodology used is based on a gas chromatography – mass spectrometry search of
the prepared compounds in the residue obtained after ethylation, thioacidolysis, and desulfurization of the pulps. Detec-
tion of biphenyl I (≈4 × 10–6 mol g–1) in unbleached and NaBH4-reduced pulps is indicative of the presence of pheno-
lic coniferaldehyde units in these pulps. Traces of biphenyl II, found in the peroxide-bleached pulp, probably came
from ferulic acid units formed by oxidation of coniferaldehyde by H2O2. No biphenyl ether III or benzylaryl ether IV
were detected in the three pulps. This result indicates that phenolic phenylpropenol units are not present in softwood
mechanical pulps and do not contribute to the fast part of their photoyellowing.
Key words: mechanical pulp, photoyellowing, phenol, coniferyl alcohol, biphenyl.
Résumé : Trois biphenyls (I, II, III) et un éther benzylaryle (IV) ont été synthétisés afin de détecter et quantifier la
présence de structures phénylpropénol dans des pâtes mécaniques de bois tendre non-blanchie, blanchie avec du
peroxyde d’hydrogène ou réduite avec du borohydrure de sodium. La méthodologie utilisée est basée sur une recher-
che, par chromatographie – spectrométrie de masse, des composés préparés dans le résidu obtenu après éthylation,
thioacidolyse et désulfuration des pâtes. La détection du biphényl I (≈4 × 10–6 mol g–1) dans la pâte non-blanchie et
dans celle réduite par NaBH4 indique la présence de motifs coniféraldéhyde phénolique dans ces pâtes. Les traces du
biphényl II, trouvées dans la pâte blanchie avec H2O2, proviennent vraisemblablement de structures acide férulique
formées par oxydation par H2O2 d’unités coniféraldéhyde. L’absence de détection du biphényl III ou de l’éther
benzylaryle dans les trois pâtes indique que les unités phénylpropénol phénolique ne sont pas présentes dans les pâtes
mécaniques de bois tendre et ne contribue pas à la phase rapide de leur photojaunissement.
Mots clés : pâte à papier, lignine, photojaunissement, phénols, alcool coniférylique. Ruffin et al. 1231
Introduction
photobleaching of the fluorescent chromophores, the materi-
als exhibited a photochromic effect (10). The borohydride-
reduced woods performed differently in the photobleaching
experiment from their paper counterpart. These subtle differ-
ences were attributed to stilbene chromophores formed by
mechanochemistry present in paper and not in the wood
(10). Nevertheless, studies on the effect of mechanical refin-
ing on the formation of photoactive chromophores in black
spruce chips casts doubt on this effect (11).
When lignin-rich pulps are bleached with alkaline hydro-
gen peroxide, β-1 units are transformed into stilbenes (12),
and α-carbonyl phenols and coniferaldehydes are converted
into methoxyhydroquinones (13, 14). All these chromophores
are considered to have a key role in the photoyellowing of
bleached lignin-rich pulps (15). Lee and Sumimoto (16) con-
sidered that para-hydroxybenzoquinone derivatives, includ-
ing stilbene-, biphenyl-, or diphenylether-conjugated structures,
were the major ones responsible for color reversion of pulps.
However, recent studies on light-induced brightness loss of
pulps, which were targeted on the role of stilbene phenols
formed from β-1 units (17) and stilbenes (including hydro-
quinone moieties formed from β-5 units (18)), indicate a mi-
nor role of these structural elements.
High-yield pulps are obtained by the mechanical refining
of wood. This defibration of lignocellulosic material might
induce some chemical modification and new chemical struc-
tures might be formed. Phenylcoumaran and β-1 units are
turned into stilbenes (1–3), β-O-4 entities are converted into
para-hydroxybenzaldehydes (4), and coniferyl alcohols cre-
ate α,β-unsaturated groups (5). Acidic treatment generates
stilbenes (6) and phenylcoumarones, which are very sensi-
tive to UV light (7, 8).
Comparison of the fluorescence emission between stone-
ground wood pulp and native wood (abies (fir)) (9) leads to
the conclusion that pulp and wood behave similarly. Reduc-
tion of the material with sodium borohydride enhanced the
fluorescence due to coniferyl alcohol and biphenyl units. It
was observed that when paper and wood were subject to
Received 19 March 2002. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 30 August 2002.
B. Ruffin, S. Grelier, A. Nourmamode, and A. Castellan.1
Laboratoire de Chimie des Substances Végétales, Université
Bordeaux 1, 351 cours de la Liberation, F-33405 Talence,
France.
According to model studies (8, 19), phenolic coniferyl al-
cohol units were found to be very light-sensitive and might
1Corresponding author (e-mail: a.castellan@ipin.u-bordeaux.fr).
Can. J. Chem. 80: 1223–1231 (2002)
DOI: 10.1139/V02-123
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Can. J. Chem. Vol. 80, 2002
Fig. 1. Compounds obtained by thioacidolysis followed by desulfurization (Raney nickel) of coniferyl alcohol and coniferaldehyde (22, 24).
participate in the photoyellowing of bleached high-yield
pulps. In our continuous effort to determine structures at the
origin of the fast photoyellowing of lignocellulosic materials
(17 to 18, 20 to 21), we present in this paper an attempt to
detect, in pulp, the phenolic phenylpropenol moiety included
in biphenyl or diarylether structures. The methodology used
was thioacidolysis, followed by desulfurization with Raney
nickel, GC–MS analysis, and comparison of the data with
those from authentic samples synthesized for the purpose.
as structures A and B, and diarylether units, such as structure
C (Fig. 2). Biphenyl structures were found to exist in high
proportion in lignin in the form of dibenzodioxocin (25).
By thioacidolysis followed by desulfurization, structure A
should lead to compounds I–III (Fig. 2). The same treat-
ment applied on structure B should give compounds I and
III. The syntheses of the biphenyl model compounds I–III
and the diarylether model IV (representative of structure C)
(Fig. 2) were completed. Compound V, isomer of III, was
not considered because it is not formed from structure B,
and unit A is accounted for by dimers I–III. The investiga-
tion was made on three pulps: unbleached mechanical soft-
wood pulp (MSP) (mainly from spruce), hydrogen peroxide
bleached MSP, and sodium borohydride reduced MSP (vide
infra).
Results and discussion
General
During irradiation of thermomechanical pulps, Pan et al.
(22) observed the formation of coniferyl aldehydes and the
disappearance of coniferyl alcohols. Moreover, fluorescence
studies on milled wood lignin (MWL) have revealed a great
reactivity of coniferyl alcohol structures under irradiation
(23); in particular, they are turned into coniferyl aldehydes
and other structures that emit at 500 nm. It was observed
that coniferyl aldehydes deactivate the emission at 400 nm
caused by biphenyl structures. Based on this observation, we
decided to attempt to detect and quantify phenolic
phenylpropenols in high yield pulps and follow their evolu-
tion under UV–vis irradiation.
Synthesis of compounds
Synthesis of compound I is described in Fig. 3. The key
step in this synthesis is the monoprotection of one of the two
phenoxyl groups of the biphenyl. Eugenol is converted into
the dehydrodimer by oxidative coupling with potassium
ferricyanide. The compound obtained is then hydrogenated
and monoethylated by treatment with diethylsulfate with so-
dium hydroxide, thanks to the different acidity between the
two phenolic groups (26).
Compound II could not be obtained by isomerization of
the corresponding isomer at high temperature (unlike iso-
eugenol, which is obtained from eugenol by treatment with
sodium hydroxide in diethylene glycol (27)). Other attempts
with different solvents (DMSO, THF) or bases (t-BuOK)
were conducted without success. Compound II was prepared
according to the route described in Fig. 4. GC–MS analysis
of compound II revealed the presence of four propene chain
isomers in the relative ratio 36:30:19:15. According to their
relative stability, the highest and lowest figures could be as-
signed to E,E and Z,Z isomers.
A widespread method for analysis and quantitative deter-
mination of lignin units is thioacidolysis; this method is a
depolymerization of lignin by ethanethiol in the presence of
BF3·Et2O, followed by gas chromatography separation and
mass spectrometry analysis of the products (24). For analy-
sis of lignin-condensed structures by thioacidolysis, a
desulfurization step with Raney nickel is necessary, because
condensed structures are too heavy to be analyzed by GC.
However, reductive treatment leads to the formation of a
propyl chain for both coniferyl alcohol and coniferyl alde-
hyde (Fig. 1) (24).
To differentiate phenolic coniferyl alcohol elements from
non-phenolic coniferyl alcohol units, the pulp was ethylated.
In this study, we looked for coniferyl alcohol structures in-
cluded in the lignin macrostructure as biphenyl elements, such
Compound III was synthesized according to the scheme
described in Fig. 5. The key step for this synthesis is the
Kharasch reaction between a Grignard reagent and an aryl
halide (28, 29).
© 2002 NRC Canada

Ruffin et al.
1225
Fig. 2. Phenolic phenylpropenol units present in softwood pulp and structures resulting from thioacidolysis and desulfurization treat-
ments.
Compound IV was obtained by the reaction sequence de-
scribed in Fig. 6. The yield (3.5%) is very low because the
main product formed by this procedure was compound 2.
The latter is formed by oxidative coupling of compound 10
in the presence of Cu2+ (30).
Analysis of the pulps
To characterize only phenolic coniferyl alcohol structures,
the pulp was treated with diethylsulfate in alkaline medium —
this is a very efficient reaction to etherify phenols. Then
the pulps were thioacidolysed and desulfurized. GC–MS
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Can. J. Chem. Vol. 80, 2002
Fig. 3. Synthetic scheme of compound I.
Fig. 4. Synthetic scheme of compound II.
analyses are reported in Table 1 for unbleached and H2O2-
and NaBH4-treated pulps.
Among the four studied compounds, only compound I
was found in unbleached and reduced pulps, in minute quan-
tity (≈4 × 10–6 mol g–1), which represents an order of mag-
nitude higher than that found for stilbene phenols in perox-
ide bleached pulps (17). In peroxide bleached pulp, com-
pound I was not detected. It is likely that compound I is not
formed from phenylpropenol units but from phenylpropenal
ones, these structures being degraded by hydrogen peroxide.
© 2002 NRC Canada

Ruffin et al.
1227
Fig. 5. Synthetic scheme of compound III.
Fig. 6. Synthetic scheme of compound IV.
Traces of compound II were detected only for peroxide
treated pulp in the form of two isomers, E,E and Z,E or E,Z.
These isomers might be formed from cinnamic acid struc-
tures generated by the action of hydrogen peroxide on
coniferaldehyde units. The lack of detection of compounds
III and IV would indicate a very low content of phenolic
coniferyl alcohol units or an inefficient ethylation of phe-
nols, which is improbable considering the detection of com-
pound I and the large excess of diethylsulfate used to treat
pulps.
The lack of detection of compounds III and IV indicates
that phenolic phenylpropenol units are not present in large
amounts in bleached softwood mechanical pulps and there-
fore do not contribute to their fast photoyellowing.
Experimental
General
Melting points were measured with a Mettler FP62 heat-
ing block. NMR spectra were recorded on a Bruker DPX200
(1H, 13C) spectrometer (reference Me4Si, solvent CDCl3).
The IR and UV absorption spectra were performed on
PerkinElmer Paragon 1000 PC and Hitachi U-3300 spec-
trometers, respectively. Mass spectra were obtained using a
VG Micromass Autospec Q instrument incorporating an
electron ionization source (70 eV).
The usual chemicals were obtained from Aldrich, and
they were used without further purification. The synthesized
compounds were purified by column chromatography on
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Can. J. Chem. Vol. 80, 2002
Table 1. Detection and quantification by GC–MS of compounds I, II, III, and IV in softwood mechanical pulps after thioacidolysis
and desulfurization.
Pulp and (or) compounds (1 × 10–6 mol g–1)
I
II
III
IV
Untreated pulp
H2O2-bleached pulp
NaBH4-reduced pulp
3.7
—
4.5
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
Trace of two isomers
n.d.
Note: n.d. = not detected
silica gel 60 (70−200 mesh) using the appropriate eluents.
Thioacidolysis and Raney nickel treatment of pulps
The solid products were crystallized after chromatography.
Thioacidolysis and desulfurization experiments were per-
formed according to a procedure described by Lapierre et al.
(24, 31). Pulp (50 mg), treated with 10 mL of thioacidolysis
solution (10 mL EtSH + 2.4 mL BF3·Et2O + 80 mL dioxan),
was heated at 100°C for 4 h under magnetic stirring. After
hydrolysis with diluted NaHCO3 solution until pH 3 to 4, the
reaction mixture was extracted with dichloromethane. To the
dichloromethane solution, docosane was added as an internal
standard for quantitative measurements. The organic phase
was washed with water, dried over magnesium sulfate, and
evaporated under vacuum. The solid residue was dissolved
in 0.5 mL of dichloromethane and reacted with 2 mL of
aqueous Raney nickel solution (50%) in 10 mL of methanol
for 4 h at 80°C. After cooling, the resulting mixture was hy-
drolyzed with hydrochloric acid (10%) and extracted with
dichloromethane. The organic phase, after washing with wa-
ter, was dried over magnesium sulfate and evaporated to
0.5 mL. The organic phase was silylated with BSTFA
(50 µL) in the presence of pyridine (10 µL) at room temper-
ature for 30 min.
Analysis of the compounds was performed by gas chro-
matography (GC) with
(Shimadzu GC 14A equipped with a CR4A Chromatopac
data analyzer) or GC (Hewlett-Packard 5890
a
flame ionization detector
chromatograph) interfaced with a mass spectrometer (VG
Micromass Autospec Q). The GC analyses were made using
capillary columns (J and W Scientific) (30 m × 0.25 mm;
film thickness, 0.25 µm; stationary phase DB-5MS). The in-
jector port temperature was set at 280°C and the detector
port temperature at 300°C (Shimadzu GC 14A). The transfer
line between the GC apparatus and the mass spectrometer
source was fixed at 220°C. The oven temperature program
(GC) started at 180°C (1 min), then rose between 180 and
300°C with a gradient of 4°C min–1, and finally was set to
300°C (30 min).
Chemical treatment of pulp
Bleaching of pulp with hydrogen peroxide
Mechanical pulp, mainly from spruce (0.5 g), kindly given
by Dr. Petit-Conil (Centre Technique du Papier, Grenoble,
France), was treated with hydrogen peroxide (30%, 0.5 mL)
and sodium hydroxide (10 mg in 50 mL of water) in a plas-
tic bag. After being heated at 50°C for 4 h, the pulp was
washed with distilled water, diluted hydrochloric acid (5%),
and water to bring the pH near 5. The pulp was filtered and
keep at 4°C before etherification with diethylsulfate.
Syntheses
Synthesis of compound I
5,5′-Diallyl-2,2′-dihydroxy-3,3′-dimethoxybiphenyl
(dihydrodiisoeugenol) (1)
A solution of eugenol (5.0 g, 30.5 mmol) and sodium ace-
tate (9.0 g, 110.0 mmol) in water (200 mL) was treated,
dropwise, with a solution of potassium ferricyanide (20.0 g,
60.8 mmol) in water (200 mL). After being stirred at room
temperature for 3 h, the reaction mixture was filtered and the
solid product was purified by crystallization in CH2Cl2 – pe-
troleum ether (PET), affording the expected biphenyl 1 as
beige crystals (3.8 g), yield 75%; mp 107°C (lit. (32) value
Reduction of pulp with NaBH4
Mechanical pulp mainly from spruce (0.5 g) was reacted
with sodium borohydride (0.5 g in 20 mL of water). After
being stirred at room temperature for 2 days, the pulp was
washed with hydrochloric acid (5%) and water to bring the
pH near 5. The pulp was filtered and kept at 4°C before
etherification with diethylsulfate.
1
mp +106°C). H NMR (CDCl3) δ: 3.40 (d, 4H, CH2), 3.84
(s, 6H, OCH3), 5.17 (d, 4H, =CH2), 6.0 (m, 4H, CH), 6.9–
7.0 (m, 4H, ArH). 13C NMR (CDCl3) δ: 40.0 (CH2), 56.1
(OCH3), 110.7 (CH Ar), 115.7 (=CH2), 123.1 (CH Ar),
124.3 (C Ar), 131.9 (C Ar), 137.7 (=CH), 140.9 (C Ar),
147.2 (C Ar).
Ethylation of pulps
The defiberized pulps (3 g) in suspension in water
(100 mL) were treated under magnetic stirring and a nitro-
gen atmosphere with 5 mL of 10% sodium hydroxide solu-
tion. The mixtures were heated at 40°C for 15 min and then
diethylsulfate (2 mL) was added. The stirring was continued
for 1 h and then the alternating addition of sodium hydrox-
ide and diethylsulfate was repeated. This cycle was repeated
once more. Then the pulp was successively washed with di-
lute hydrochloric acid (5%) and distilled water (to pH ≈ 5),
and filtered. The pulp was first dried in an oven at 40°C and
then over P2O5 under vacuum before thioacidolysis treat-
ment.
2,2′-Dihydroxy-3,3′-dimethoxy-5,5′-di-n-propylbiphenyl (2)
Hydrogenation of compound 1 (2.0 g, 6.1 mmol) in meth-
anol (75 mL) containing 0.2 g of carbon palladium (10%)
was accomplished by treating the mixture under hydrogen
pressure (180 bar) for 24 h at room temperature. The mix-
ture, after filtration, afforded a beige solid (1.8 g, 90%); mp
152°C (lit. (33) value mp +152°C). IR (KBr) (cm–1): 850,
1050, 1145, 1230, 1260, 1375, 1425, 2920, 2945, 3300.
1H NMR (CDCl3) δ: 0.95 (t, 6H, CH3), 1.63 (m, 4H, CH2),
2.55 (t, 4H, CH2), 3.91 (s, 6H, OCH3), 6.03 (s, 2H, OH), 6.7
© 2002 NRC Canada

Ruffin et al.
1229
(m, 4H, ArH). 13C NMR (CDCl3) δ: 13.9 (CH3), 24.8 (CH2),
37.9 (CH2), 56.1 (OCH3), 110.6 (CH Ar), 122.9 (CH Ar),
124.4 (C Ar), 134.7 (C Ar), 140.5 (C Ar), 147.1 (C Ar).
2-Ethoxy-4,4 ′-diformyl-2 ′-acetoxy-3,3′-dimethoxybiphenyl (5)
A solution of 4 (3.3 g, 9.9 mmol) in CH2Cl2 (50 mL) was
treated with triethylamine (5 mL, 36.1 mmol), acetic anhy-
dride (1.4 mL, 12.6 mmol), and traces of 4-dimethyl-
aminopyridine (DMAP). After being refluxed for 20 h, the
mixture was reacted with water. The aqueous layer was ex-
tracted with CH2Cl2. The combined organic layers were
washed with water, dried over MgSO4, filtered, and concen-
trated, affording the expected compound 5 (3.5 g), yield
95%, as a pale yellow solid; mp 127°C. IR (KBr) (cm–1):
740, 890, 1040, 1130, 1180, 1270, 1380, 1576, 1700, 1765.
1H NMR (CDCl3) δ: 1.08 (t, 3H, CH3), 2.10 (s, 3H, OAc),
3.92 (q, 2H, OCH2), 3.94 (s, 3H, OCH3), 3.95 (s, 3H,
OCH3), 7.2–7.5 (m, 4H, ArH), 9.87 (s, 1H, CHO), 9.95 (s,
1H, CHO).
2-Hydroxy-2′-ethoxy-3,3′-dimethoxy-5,5′-di-n-propylbiphenyl
(I)
A solution of compound 2 (600 mg, 1.82 mmol) in THF
(50 mL) was treated with a solution of potassium hydroxide
(102 mg, 1.82 mmol) and diethylsulfate (0.5 mL, 4.0 mmol).
After being stirred at 70°C for 12 h, the solution was reacted
with a solution of hydrochloric acid (10%). The aqueous
layer was extracted with CH2Cl2. The combined organic lay-
ers were washed with water, dried over MgSO4, filtered, and
concentrated. The product was purified by chromatography
on silica gel (eluent Et2O−PET, 60:40) affording the ex-
pected compound I (400 mg, 62%) as a pale yellow oil. IR
(NaCl) (cm–1): 840, 1050, 1140, 1230, 1460, 1580, 2870,
Ethyltriphenylphosphonium iodide (6)
1
A solution of iodoethane (3.0 g, 19.1 mmol) in toluene
(50 mL) was treated with triphenylphosphine (6.0 g,
23.0 mmol) at 80°C for 3 h. The resulting white product was
filtered and dried, affording the expected salt 6 (6.8 g), yield
84%; mp 168°C (lit. (35) value mp +168 to 169°C).
2930, 2960. H NMR (CDCl3) δ: 0.84 (t, 3H, CH3), 0.86 (t,
3H, CH3), 1.02 (t, 3H, CH3), 1.55 (m, 4H, 2×CH2), 2.46 (t,
2H, CH2), 2.48 (t, 2H, CH2) 3.74 (q, 2H, OCH2), 3.78 (s,
3H, OCH3), 3.80 (s, 3H, OCH3), 6.6−6.7 (m, 4H, ArH),
6.72 (s, 1H, OH). 13C NMR (CDCl3) δ: 13.8 (CH3), 14.0
(CH3), 15.3 (CH3), 24.6 (CH2), 24.8 (CH2), 37.8 (CH2), 38.0
(CH2), 55.9 (OCH3), 56.1 (OCH3), 69.9 (OCH2), 111.2 (CH
Ar), 111.7 (CH Ar), 122.9 (CH Ar), 123.4 (CH Ar),
128.2 (C Ar), 132.6 (C Ar), 134.3 (C Ar), 139.2 (C Ar),
141.2 (C Ar), 142.4 (C Ar), 148.5 (C Ar), 152.6 (C Ar). MS
(TMS derivative): 430 ([M]+·,100%), 401 (10%), 387 (14%),
357 (9%), 73 (31%).
2-Ethoxy-4,4 ′-diformyl-2′-acetoxy-3,3′-dipropenylbiphenyl (7)
An n-butyl lithium solution in n-hexane (2.5 mol L–1,
5.2 mmol) was added to a solution of the phosphonium salt
6 (2.1 g, 5 mmol) in anhyd THF (30 mL) under an N2 atmo-
sphere and the mixture was stirred at –70°C for 15 min. The
resulting red solution was treated with a solution of aldehyde
5 (0.9 g, 2.4 mmol) in anhyd THF (20 mL). After being
stirred at room temperature for 2 h, the mixture was reacted
with a solution of hydrochloric acid (10%). The aqueous
layer was extracted with CH2Cl2. The combined organic lay-
ers were washed with water, dried over MgSO4, filtered, and
concentrated. The product was purified by chromatography
on silica gel (eluent CH2Cl2) affording the expected com-
pound 7 (0.6 g, 63%) as a yellow solid; mp 127°C. IR (KBr)
(cm–1): 760, 790, 960, 1050, 1140, 1460, 1580, 1700, 1770,
Synthesis of compound II
4,4′-Diformyl-2,2′-dihydroxy-3,3′-dimethoxybiphenyl (3)
Vanillin (5.0 g, 33 mmol) in hot water (200 mL) was
treated by ferrous sulfate (200 mg, 0.7 mmol) and potassium
persulfate (5.0 g, 20 mmol) at 100°C for 2 h. The resulting
product was filtered and dried in an oven, affording the ex-
pected compound 3 (4.3 g, 86%); mp 304°C (lit. (34) value
mp +305°C). IR (KBr) (cm–1): 750, 850, 1050, 1150, 1260,
1420, 1460, 1590, 1680, 3260. 1H NMR (DMSO) δ: 3.98 (s,
6H, OCH3), 7.4 (s, 4H, ArH), 9.85 (s, 2H, CHO). 13C NMR
(DMSO) δ: 56.0 (OCH3), 109.0 (CH Ar), 124.5 (CH Ar),
127.9 (C Ar), 128.2 (C Ar), 148.1 (C Ar), 150.3 (C Ar),
191.1 (CHO).
1
2950. H NMR (CDCl3) δ: 1.1 (t, 3H, CH3), 1.6 (2d, 6H,
CH3), 2.0 (s, 3H, OAc), 3.9 (m, 8H, 2 × OCH3 and OCH2),
5.5–6.0 (m, 4H, CH=CH), 6.8 (m, 4H, ArH). 13C NMR
(CDCl3) δ: 15.4 (CH3), 20.4 (Ac), 56.0 (OCH3), 56.3
(OCH3), 69.6 (OCH2), 109.7 (CH Ar), 110.1 (CH Ar), 127.1
(CH Ar), 127.4 (CH Ar), 130.7 (C Ar), 132,0 (C Ar), 132.5
(C Ar), 134.3 (C Ar), 190.8 (CHO), 191.0 (CHO).
2-Ethoxy-4,4′-diformyl-2′-hydroxy-3,3′-dimethoxybiphenyl (4)
2-Ethoxy-4,4′-diformyl-2′-hydroxy-3,3′-dipropenylbiphenyl (II)
Dehydrodivanillin 3 (3.0 g, 9.9 mmol) in THF (100 mL)
was treated with a solution of potassium hydroxide (0.6 g,
10.0 mmol) in water (10 mL) and iodoethane (3.2 g,
20.5 mmol). After being refluxed for 6 h, the mixture was
reacted with a solution of hydrochloric acid (10%). The
aqueous layer was extracted with CH2Cl2. The combined or-
ganic layers were washed with water, dried over MgSO4, fil-
tered, and concentrated, affording the expected compound 4
(3.3 g, 100%) as a pale yellow solid; mp 195°C. IR (KBr)
(cm–1): 740, 890, 1040, 1150, 1180, 1260, 1420, 1580, 1700,
A solution of 7 (600 g, 1.52 mmol) in methanol (50 mL)
was treated with potassium carbonate (250 mg, 1.81 mmol).
After being stirred at room temperature for 4 h, the mixture
was reacted with a solution of hydrochloric acid (10%). The
aqueous layer was extracted with CH2Cl2. The combined or-
ganic layers were washed with water, dried over MgSO4, fil-
tered, and concentrated. The product was purified by
chromatography on silica gel (eluent CH2Cl2–Et2O, 98:2) af-
fording the expected compound II (450 mg, 80%) as a pale
yellow oil; mp 127°C. 1H NMR (CDCl3) δ: 1.1 (t, 3H, CH3),
1.8 (d, 3H, CH3), 1.9 (d, 3H, CH3), 3.9 (m, 8H, 2 × OCH3
and OCH2), 5.6−7.0 (m, 8H, ArH, and CH=CH). Four
stereoisomers displaying the same mass spectrum were iden-
tified by GC–MS (retention time: 18.8 (30%), 19.7 (36%),
1
3250. H NMR (CDCl3) δ: 1.11 (t, 3H, CH3), 3.98 (s, 3H,
OCH3), 4.01 (q, 2H, OCH2), 4.06 (s, 3H, OCH3), 6.59 (s,
1H, OH), 7.4−7.5 (m, 4H, ArH), 9.86 (s, 1H, CHO), 9.92 (s,
1H, CHO).
© 2002 NRC Canada

1230
Can. J. Chem. Vol. 80, 2002
20.0 (15%), and 21.0 min (19%)). MS (TMS derivative):
426 ([M]+, 100%), 383 (12%), 73 (35%).
for 2 h. The solvent was removed and compound 11 (3.0 g,
100%) was obtained as a beige solid; mp 83°C (lit. (36) value
mp +82.5 to 83.5°C). IR (KBr) (cm–1): 820, 860, 960, 1040,
1150, 1200, 1270, 1500, 1590, 2870, 2930, 2950, 3420.
1H NMR (CDCl3) δ: 0.96 (t, 3H, CH3), 1.60 (q, 2H, CH2),
2.60 (t, 2H, CH2), 3.85 (s, 3H, OCH3), 6.66 (s, 1H, ArH),
7.08 (s, 1H, ArH). 13C NMR (CDCl3) δ: 13.8 (CH3), 23.5
(CH2), 37.9 (CH2), 56.1 (OCH3), 112.2 (CH Ar), 114.6 (C-Br),
118.4 (CH Ar), 133.3 (C Ar), 144.3 (C Ar), 145.9 (C Ar).
Synthesis of compound III
4-Ethoxy-5-iodo-3-methoxybenzaldehyde (8)
5-Iodovanillin (3.0 g, 10.8 mmol) in THF (75 mL) was
treated with a solution of potassium hydroxide (1.0 g,
17.8 mmol) in water (10 mL) and iodoethane (4.0 g,
25.6 mmol). After being refluxed for 6 h, the mixture was
reacted with water. The aqueous layer was extracted with
CH2Cl2. The combined organic layers were washed with a
solution of hydrochloric acid (10%), dried over MgSO4, fil-
tered, and concentrated, affording the expected compound 8
(3.3 g, 100%) as white crystals; mp 42°C. IR (KBr) (cm–1):
590, 670, 790, 1040, 1150, 1270, 1390, 1460, 1560, 1580,
1-Bromo-2-ethoxymethoxy-3-methoxy-5-propylbenzene (12)
A solution of 11 (2.9 g, 11.8 mmol) in DMF (120 mL)
was treated with potassium carbonate (9.0 g, 65.2 mmol)
and chloromethylethylether (3.4 mL, 36.6 mmol). After be-
ing stirred at 80°C for 18 h, the mixture was reacted with a
solution of hydrochloric acid (10%). The aqueous layer was
extracted with CH2Cl2. The combined organic layers were
washed with water, dried over MgSO4, filtered, and concen-
trated. The product was purified by chromatography on sil-
ica gel (eluent CH2Cl2) affording the expected compound 12
(2.5 g, 69%) as a green oil. IR (NaCl) (cm–1): 850, 950,
1160, 1250, 1460, 1500, 2870, 2930, 2960. 1H NMR
(CDCl3) δ: 0.92 (t, 3H, CH3), 1.15 (t, 3H, CH3), 1.8 (m, 2H,
CH2), 2.8 (m, 2H, CH2), 3.78 (q, 2H, OCH2), 3.85 (s, 3H,
OCH3) 5.24 (s, 2H, OCH2O), 6.8–7.0 (m, 2H, ArH).
1
1690, 2970. H NMR (CDCl3) δ: 1.25 (t, 3H, CH3), 3.83 (s,
3H, OCH3), 4.05 (q, 2H, OCH2), 7.23 (d, 1H, ArH), 7.77 (d,
1H, ArH), 9.81 (s, 1H, CHO). 13C NMR (CDCl3) δ: 15.7
(CH3), 56.2 (OCH2), 69.5 (OCH3), 110.0 (CH Ar), 118.3
(C-I), 128.6 (CH Ar), 132.8 (C Ar), 151.0 (C Ar), 154.2
(C Ar), 169.9 (CHO).
2-Ethoxy-1-iodo-3-methoxy-5-propenylbenzene (9)
An n-butyl lithium solution in n-hexane (2.5 mol L–1,
10.0 mmol) was added to a solution of the phosphonium salt
6 (4.2 g, 10.0 mmol) in anhyd THF (50 mL) under N2 atmo-
sphere and the mixture was stirred at –70°C for 15 min. The
resulting red solution was treated with a solution of aldehyde
8 (3.0 g, 9.8 mmol) in anhyd THF (40 mL). After being
stirred at room temperature for 2 h, the mixture was reacted
with a solution of hydrochloric acid (10%). The aqueous
layer was extracted with CH2Cl2. The combined organic lay-
ers were washed with water, dried over MgSO4, filtered, and
concentrated. The product was purified by chromatography
on silica gel (eluent CH2Cl2) affording the expected com-
pound 9 (2.5 g), yield 80%, as a pale yellow solid; mp 33°C.
IR (KBr) (cm–1): 780, 870, 960, 1050, 1140, 1230, 1250,
2′-Ethoxy-2-ethoxymethoxy-3,3′-dimethoxy-5′-propenyl-5-
propylbiphenyl (13)
Magnesium (0.2 g, 5.0 mmol) and two crystals of iodine
in anhyd THF (5 mL) under an N2 atmosphere were treated
with a solution of 9 (1.0 g, 3.1 mmol) in anhyd THF
(30 mL). After being stirred at 70°C for 6 h, the mixture was
transferred dropwise into a second flask charged with palla-
dium (II) bis-(triphenylphosphine) dichloride (0.2 mg,
0.28 mmol), compound 12 (0.95 g, 3.1 mmol), and 20 mL of
anhyd THF. After being stirred at 70°C for 8 h, the mixture
was reacted with a solution of hydrochloric acid (10%). The
aqueous layer was extracted with CH2Cl2. The combined or-
ganic layers were washed with water, dried over MgSO4, fil-
tered, and concentrated. The product was purified by
chromatography on silica gel (eluent CH2Cl2), affording the
expected compound 13 (800 mg, 61%) as an orange oil.
1H NMR (CDCl3) δ: 0.94 (t, 3H, CH3), 1.12 (t, 3H, CH3),
1.35 (m, 3H, CH3), 1.47 (m, 2H, CH2), 1.72 (2d, 3H,
CH3-CH=), 3.79 (t, 2H, OCH2), 3.87 (s, 3H, OCH3), 3.89 (s,
3H, OCH3), 4.15 (s, 2H, OCH2), 5.22 (s, 2H, OCH2O),
5.8–6.2 (m, 2H, CH=CH), 6.4–6.8 (m, 4H, ArH).
1
1510, 2950. H NMR (CDCl3) δ: 1.44 (t, 3H, CH2-CH3),
1.87 (2 × dd, 3H, CH-CH3), 3.85 (s, 3H, OCH3), 4.04 (q,
2H, OCH2), 6.0–6.4 (m, 2H, CH=CH), 6.79 (d, 1H, ArH, J =
1.72 Hz), 6.81 (d, 1H, ArH, J = 1.72 Hz). 13C NMR (CDCl3)
δ: 14.8 (CH3), 18.4 (CH-CH3), 55.8 (OCH2), 64.3 (OCH3),
108.8 (CH Ar), 112.7 (CH=), 118.7 (C-I), 123.7 (CH), 130.6
(CH), 131.1 (C Ar), 148.2 (C Ar), 149.5 (C Ar).
2-Methoxy-4-n-propylphenol (10)
Hydrogenation of eugenol (3.0 g, 18.3 mmol) in methanol
(75 mL) containing 0.3 g of carbon palladium (10%) was ac-
complished by treating the mixture under hydrogen pressure
(80 bar) for 24 h at 40°C. The mixture, after filtration, af-
forded compound 10 (2.7 g, 90%) as a green oil. IR (NaCl)
(cm–1): 795, 820, 1030, 1120, 1150, 1270, 1430, 1460, 1500,
1600, 2870, 2930, 2960, 3500. H NMR (CDCl3) δ: 0.7 (t,
3H, CH3), 2.25 (t, 2H, CH2), 2.85 (t, 2H, CH2), 3.45 (s, 3H,
OCH3), 5.3 (s, 1H, OH), 6.2−6.7 (m, 3H, ArH).
2′-Ethoxy-2-hydroxy-3,3′-dimethoxy-5′-propenyl-5-propyl-
biphenyl (III)
A solution of 13 (500 mg, 1.2 mmol) in CH2Cl2 (30 mL)
was treated with trifluoroacetic acid (0.09 mL, 1.2 mmol).
After being stirred at room temperature for 4 h, the mixture
was reacted with water. The aqueous layer was extracted
with CH2Cl2. The combined organic layers were washed
with water, dried over MgSO4, filtered, and concentrated to
afford the expected compound III (Z isomer, 200 mg, 46%)
as a yellow oil. IR (NaCl) (cm–1): 960, 1050, 1230, 1250,
1
2-Bromo-6-methoxy-4-n-propylphenol (11)
1
A solution of bromine (0.7 mL, 13.6 mmol) in CHCl3
(60 mL) was added dropwise to a solution of 10 (2.0 g,
12.0 mmol) in CHCl3 (100 mL) at 0°C. Once the addition
was completed, the mixture was stirred at room temperature
1500, 2950, 3600. H NMR (CDCl3) δ: 0.92 (t, 3H, CH3),
1.35 (m, 3H, CH3), 1.49 (m, 2H, CH2), 1.75 (2d 3H, CH3-
CH=), 2.64 (m, 2H, CH2), 3.88 (s, 3H, OCH3), 3.91 (s, 3H,
OCH3), 4.21 (s, 2H, OCH2O), 5.8–6.2, m, CH=CH), 6.4–6.8
© 2002 NRC Canada

Ruffin et al.
1231
(m, 4H, ArH). 13C NMR (CDCl3) δ: 13.8 (CH3), 14.5 (CH3),
17.7 (CH3), 24.2 (CH2), 37.5 (CH2), 55.2 (OCH3), 56.6
(OCH3), 64.8 (OCH2), 112.1 (CH), 117.0 (CH), 120.0 (CH),
121.5 (CH), 124.1 (CH), 126.8 (CH), 128.3 (C Ar), 130.5
(C Ar), 130.8 (C Ar), 131.4 (C Ar), 144.3 (C Ar), 145.9
(C Ar), 147.2 (C Ar), 149.1 (C Ar). MS (TMS derivative):
428 ([M]+,100%), 399 (10%), 385 (15%), 73 (32%).
2. D.Y. Lee, M. Matsuoka, and M. Sumimoto. Proceedings: Int.
Symp. Wood Pulping Chem. 5th, Raleigh, NC, U.S.A. 21 (1989).
3. Z. Wu, M. Matsuoka, D.Y. Lee, and M. Sumimoto. Mokuzai
Gakkaishi, 37, 164 (1991).
4. D.Y. Lee and M. Sumimoto. Holzforschung, 44, 347 (1990).
5. D.Y. Lee, S. Tachibana, and M. Sumimoto. Cellulose Chem.
Technol. 22, 201 (1988).
6. S. Li and K. Lundquist. Holzforschung, 53, 39 (1999)
7. A. Castellan, N. Colombo, A. Nourmamode, J. Zhu, D. Lachenal,
R.S. Davidson, and L. Dunn. J. Wood Chem. Technol. 10, 461
(1990).
8. C. Noutary, P. Fornier de Violet, J. Vercauteren, and A.
Castellan. (a) Res. Chem. Intermed. 21, 223 (1995); (b) Res.
Chem. Intermed. 21, 247 (1995).
2-Ethoxy-3,2′-dimethoxy-5-propenyl-4′-propyldiarylether (IV)
A solution of 10 (560 mg, 3.4 mmol) in pyridine (15 mL)
was treated with sodium hydride (90 mg, 3.7 mmol) and
copper bromide (490 mg, 3.4 mmol). Then compound 9
(550 mg, 1.7 mmol) was added. After being stirred at 125°C
for 18 h, the mixture was reacted with a solution of hydro-
chloric acid (10%). The aqueous layer was extracted with
CH2Cl2. The combined organic layers were washed with wa-
ter, dried over MgSO4, filtered, and concentrated. The prod-
ucts were purified by chromatography on silica gel (eluent
CH2Cl2) affording 2 (360 mg, 59%) as white crystals; mp
152°C (lit. (33) value mp +152°C), and compound IV
(20 mg, 3.5%) as a pale oil. IR (NaCl) (cm–1): 790, 1040,
1210, 1260, 1420, 1460, 1500, 1590, 2870, 2930, 2960.
1H NMR (CDCl3) δ: 0.95 (t, 3H, CH3), 1.27 (t, 3H, CH3),
1.62, 1.80, 2.56, 3.80, 3.82 (s, 3H, OCH3), 3.86 (s, 3H,
OCH3), 4.10 (q, 2H, OCH2), 6.0 to 6.8 (m, 8H, ArH, and
CH=CH). 13C NMR (CDCl3) δ: 13.8 (CH3), 15.4 (CH3),
18.2 (CH3), 24.7 (CH2), 29.7 (CH2), 37.8 (OCH2), 55.8
(OCH3), 55.9 (OCH3), 104.3 (CH Ar), 109.0 (CH Ar), 112.9
(CH Ar), 119.2 (CH Ar), 120.6 (CH Ar), 125.1 (CH Ar),
130.5 (CH Ar), 133.3 (C Ar), 138.6 (C Ar), 139.5 (C Ar),
143.7 (C Ar), 148.1 (C Ar), 150.3 (C Ar), 153.9 (C Ar). MS:
356 ([M]+,100%), 327 (20%), 296 (34%), 150 (31%).
9. A. Castellan, H. Choudhury, R.S. Davidson, and S. Grelier. J.
Photochem. Photobiol. A, 81, 117 (1994).
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Photochem. Photobiol. A, 81, 123 (1994).
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D.G. Gray. J. Pulp Pap. Sci. 23, J305 (1997).
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(b) W.J. Leigh, T.J. Lewis, V. Lin, and J.A. Postigo. Can. J.
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13. S. Omori and C.W. Dence. Wood Sci. Technol. 15, 113 (1981).
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(1980).
15. C. Heitner. ACS Symp. Ser. 531, 1 (1993).
16. D.Y. Lee and M. Sumimoto. Holzforschung, 45 (supplement),
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17. B. Ruffin, A. Castellan, S. Grelier, A. Nourmamode, S. Riela,
and V. Trichet. J. Appl. Polym. Sci. 18, 333 (1998).
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Chem. A, 103, 11 136 (1999).
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22. X. Pan, D. Lachenal, C. Lapierre, and B. Monties. Proceed-
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23. A. Castellan, A. Nourmamode, C. Noutary, C. Belin, and P.
Fornier de Violet. J. Wood Chem. Technol. 12, 19 (1992).
24. C. Lapierre, B. Pollet, and B. Monties. Phytochemistry, 30,
659 (1991).
Three biphenyl dimers (I–III) and one benzylaryl ether
(IV) were synthesized to show the presence and the impor-
tance of phenolic coniferyl alcohol structures in the
photoyellowing of high-yield pulps. The dimer I, incorporat-
ing two propyl chains, was detected in unbleached and so-
dium borohydride-reduced high-yield pulps in small
amounts (≈4 × 10–6 mol g–1). It is probably formed by
thioacidolysis and Raney nickel treatments from phenolic
biphenyl bearing coniferyl aldehyde moieties. Biphenyl II,
which includes two propenyl chains, was detected in small
amounts in peroxide bleached high-yield pulps, in the form
of two stereoisomers. Biphenyl II probably comes from a
ferulic-acid-type structure obtained from an oxidized pro-
penal chain. No arylether IV or biphenyl III compounds
were detected. This result probably indicates that phenolic
phenylpropenol units are not present in softwood mechanical
pulps, so they do not contribute to the photoyellowing pro-
cess. A similar conclusion was obtained by us, on the in-
volvement of stilbene phenol leucochromophores (17), and
recently confirmed by Johansson et al. (37). After this study
and others, the molecular origins of the fast photoyellowing
of high-yield pulps remains to be established.
25. P. Karhunen, J. Mikkola, A. Pajunen, and G. Brunow. Nord.
Pulp Pap. Res. J. 14, 123 (1999).
26. G. Aulin-Erdtman. Sven. Papperstidn. 56, 91 (1953).
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32. H.A. Jones and H.L. Haller. J. Am. Chem. Soc. 62, 2558 (1940).
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1674 (1986).
34. K. Elbs and H. Lerch. J. Prakt. Chem. 93, 1 (1916).
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© 2002 NRC Canada