Spectral assignments and reference data: A 13C NMR study of the methylol derivatives of 2,4′- and 4,4′-dihydroxydiphenylmethanes found in resol phenol-formaldehyde resins

Article abstract of DOI:10.1002/mrc.1089

A total of 13 of the 16 possible methylol derivatives of 2,4′- and 4,4′-dihydroxydiphenylmethane have been synthesized, isolated, and identified. These compounds are found as intermediates in the cure process of resol phenol-formaldehyde (PF) resins. Analysis of the ¹³C NMR spectra (in acetone-d₆) of these compounds provided a way to evaluate the seven methylolphenol ring types (methylol derivatives of 2-hydroxyphenyl and 4-hydroxyphenyl rings) found in typical resol PF resins using the ipso carbon region from 150 to 160 ppm. A simple diagnostic test was developed using the chemical shift values of the methylol methylene carbon atoms to identify the presence of intermediates containing either a 2-hydroxyphenyl or a 4-hydroxyphenyl ring. Using these data it is now possible to analyze the major components in extracted prepreg PF resins. Copyright

Full text of DOI:10.1002/mrc.1089

MAGNETIC RESONANCE IN CHEMISTRY
Magn. Reson. Chem. 2002; 40: 747–751
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/mrc.1089
Spectral Assignments and Reference Data
A 13C NMR study of the methylol derivatives
OH
of 2,4ꢀ- and 4,4ꢀ-dihydroxydiphenylmethanes
A
A
A
A
1
1
1′
1′
found in resol phenol–formaldehyde resins
4
4
4′
4′
OH
HO
OH
Thomas H. Fisher,1∗ Ping Chao,2 Cindy G. Upton3 and
Anthony J. Day4
A
A
A
A
4,4′-Dihydroxydiphenylmethanes (1 - 6)
[A = CH2OH (methylol) (m) or H]
2,4′-Dihydroxydiphenylmethanes (7-18)
1
Department of Chemistry, Mail Stop 9573, Mississippi State University,
Mississippi State, MS 39762, USA
Compd 3
5
3
′
5
′
Compd 3
5
3
′
5′
2
San Fu Chemical Co., Taipei, Taiwan, R.O.C.
NASA/MSFC, FD 21, Marshall Space Flight Center, AL 35812, USA
ATK Thiokol Propulsion, PO Box 9033, Huntsville, AL 35812, USA
1 =
2 =
3 =
4 =
H
H
H
H
m
m
m
H
H
m
H
m
m
H
H
H
H
H
m
7
8
9
=
=
=
H
m
H
H
m
H
H
H
m
H
m
H
H
H
H
m
H
m
H
H
H
H
H
m
3
m
m
m
4
10 =
11 =
12 =
Received 19 April 2002; revised 15 July 2002; accepted 25 July 2002
5 =
6 =
m
m
A total of 13 of the 16 possible methylol derivatives
of 2,4ꢀ- and 4,4ꢀ-dihydroxydiphenylmethane have been
synthesized, isolated, and identified. These compounds
are found as intermediates in the cure process of
resol phenol–formaldehyde (PF) resins. Analysis of the
13C NMR spectra (in acetone-d6) of these compounds
provided a way to evaluate the seven methylolphenol
ring types (methylol derivatives of 2-hydroxyphenyl and
4-hydroxyphenyl rings) found in typical resol PF resins
using the ipso carbon region from 150 to 160 ppm. A
simple diagnostic test was developed using the chemical
shift values of the methylol methylene carbon atoms to
identify the presence of intermediates containing either a
2-hydroxyphenyl or a 4-hydroxyphenyl ring. Using these
data it is now possible to analyze the major components
in extracted prepreg PF resins. Copyright  2002 John
Wiley & Sons, Ltd.
13 =
14 =
15 =
16 =
17 =
18 =
m
H
m
m
H
m
H
m
m
H
m
m
m
m
m
m
m
m
H
H
H
m
m
m
Figure 1. The 16 possible methylol derivatives of 4,40- and
2,40-dihydroxydiphenylmethane. All but 14, 16, and 17 were prepared in
this study.
EXPERIMENTAL
Materials
4,40-Dihydroxydiphenylmethane (1), formaldehyde (37%), phenol,
and acetone-d6 were used as purchased from Aldrich Chemical Co.
2,40-Dihydroxydiphenylmethane (7) was used as purchased from
TCI America.
KEYWORDS: NMR; 1H NMR; 13C NMR; phenol-formaldehyde
resins; dihydroxydiphenylmethanes
Syntheses of compounds 2–6
4,40-Dihydroxydiphenylmethane (1), 0.797 g (4.0 mmol), 1.2 ml of
37% formaldehyde, and 2.0 ml of 0.6 M NaOH were heated for 1 h at
INTRODUCTION
Phenol-formaldehyde (PF) resins, the first totally synthetic poly-
mers, have wide commercial applications as molding compounds,
coatings, wood binders, and high-temperature ablatives.1 Sev-
eral kinetic studies of the condensation reactions of phenol and
formaldehyde have been reported,2–6 but clear experimental veri-
fication of the major intermediates formed in the PF cure process
has been difficult to obtain. The first compounds formed in base-
catalyzed PF condensation reactions are mono-, di-, and tri-methylol
(CH2OH) derivatives of phenol. Condensation of these methylolphe-
nols with themselves or with another molecule of phenol results in
dihydroxydiphenylmethanes (HO–Ar–)2CH2 that contain methy-
lol groups.6,7 Additional methylol groups can be added to these
dihydroxydiphenylmethanes by further condensation reactions with
formaldehyde.4,8
°
60 C. Products 2–6 were separated by preparative thin-layer chro-
matography (TLC) on silica gel using methanol(8)/chloroform(60).
Rf values found for compounds 2–6 are for this solvent system;
if additional elution solvent systems were used, then their Rf val-
ues are also given: compound 6 has an Rf D 0.19; compound 5,
Rf D 0.25; compound 3, Rf D 0.36, then with chloroform(9)/ethanol
(0.6)/methanol(0.7), Rf D 0.23; compound 4, Rf D 0.36, then with
chloroform(9)/ethanol(0.6)/methanol(0.7), Rf D 0.28; compound 2,
Rf D 0.48.
Syntheses of compounds 8, 10–13, 15, and 18
2,40-Dihydroxydiphenylmethane (7), 0.892 g (4.4 mmol), 1.34 ml of
37% formaldehyde, and 2.0 ml of 1.4 M NaOH were heated for 1 h. at
Earlier, we reported a 13C NMR method for the analysis of resol
PF prepolymer resins based on nine model compounds.9 In order to
analyze the next cure stage (called prepreg) more comprehensively,
it was necessary to extend the range of model compounds to include
the methylol derivatives of the dihydroxydiarylmethanes, which are
common intermediates found in this cure stage.
°
60 C. The products were separated by preparative TLC on silica gel
using methanol(1)/chloroform(10). Rf values given for compounds
8, 10–13, 15, and 18 are for this solvent system. If additional elu-
tion solvent systems were used, then their Rf values are also given:
compound 18 has an Rf D 0.12; compound 15, Rf D 0.19, then with
chloroform(2)/ethanol(2.5)/methanol(0.7), Rf D 0.55; compound 11,
Rf D 0.31; compound 12, Rf D 0.43; compound 13, Rf D 0.49;
compound 10, Rf D 0.56; compound 8, Rf D 0.64.
In this work we report 1H and 13C NMR data on 13 of the 16 pos-
sible methylol derivatives of 4,40-dihydroxydiphenylmethane (4,40-
methylenebisphenol) and 2,40-dihydroxydiphenylmethane (2[(4-
hydroxyphenyl)methyl]phenol); see Fig. 1. Analysis of these data
led to an improved NMR method for the analysis of methylolphenol
dimers and oligomers found in the cure process of PF resins.
Synthesis of 9
5-Methylol-2,40-dihydroxydiphenylmethane (9) was prepared by
the LiAlH4 reduction of 5-carboxy-2,40-dihydroxydiphenylmethane,
which was obtained from 5-bromo-2,40-dihydroxydiphenylmethane
using the procedure of Carpenter and Hunter10 and collected by
preparative TLC on silica gel using methanol(1)/chloroform(9).
5-Bromo-2,40-dihydroxydiphenylmethane was prepared from the
dehydration reaction of 5-bromo-2-methylolphenol with phenol
under acid conditions.
ŁCorrespondence to: Thomas H. Fisher, Department of Chemistry, Mail
Stop 9573, Mississippi State University, Mississippi State, MS 39762, USA.
E-mail: thf1@ra.msstate.edu
Contract/grant sponsor: NASA/MSFC.
Contract/grant sponsor: Hercules Aerospace Company.
Copyright  2002 John Wiley & Sons, Ltd.

748
Spectral Assignments and Reference Data
to be good quantitative solvents for 13C NMR analysis of PF resins
with shorter acquisition times available using added Cr(acac)3.
Reaction of 2,40-dihydroxydiphenylmethane (7) with excess
NMR experiments
All spectra were obtained on a General Electric QE-300 NMR
spectrometer at 25 C observing 1H and 13C at 300.67 MHz and
°
75.61 MHz respectively. 1H NMR spectra were collected into 32K
°
formaldehyde and base at 60 C for 1 h resulted in seven (8, 10–13,
data sets over a spectral width of 6 kHz using a 30 pulse. 13C
°
15, 18) of the 11 possible methylol derivatives of 7. Each compound
was isolated by preparative TLC on silica gel and identified by 1H
and 13C NMR. A trace of 16 was isolated and identified by 1H NMR,
but not enough was isolated to obtain a 13C NMR spectrum.
5-Methylol-2,40-dihydroxydiphenylmethane (9) was prepared
by the by LiAlH4 reduction of 5-carboxy-2,40-dihydroxydiphenyl-
methane, which was prepared from 5-bromo-2-methylolphenol by
condensation with phenol, lithiation with BuLi, and carbonation
using the procedure of Carpenter and Hunter.10 The only methylol
derivatives of 2,40-dihydroxydiphenylmethane that could not be
synthesized and identified were 14, 16, and 17. The 1H and 13C NMR
assignments of compounds 7–13, 15, and 18 are given in Table 2.
There are seven different methylolphenol ring types found
in dihydroxydiphenylmethanes 1–18, as shown in Fig. 2. These
methylolphenol ring types are called A–G here for discussion
purposes. Types A, B, and C all have the 4-hydroxyphenyl ring
system, whereas types D, E, F, and G all have the 2-hydroxyphenyl
ring system.
spectra were collected into 32K data sets over a spectral width
°
of 20 kHz using a 40 pulse and were processed using exponential
multiplication with 1 Hz line broadening. Acetone-d6 containing
(TMS) tetramethylsilane was the solvent used for all compounds.
RESULTS AND DISCUSSION
In resol PF polymerization, only methylol derivatives of 2,40-
and 4,40-dihydroxydiphenylmethanes are formed as intermedi-
ates in the cure process, and no methylol derivatives of 2,20-
dihydroxydiphenylmethane are found.6,9,11–14 To develop further
our comprehensive 13C NMR method9 to monitor the early stages
of resol PF polymerization, each of the individual methylol isomers
of 2,40- and 4,40-dihydroxydiphenylmethanes were needed as model
compounds. To this end, an attempt was made to synthesize and
isolate each of these compounds, 1–18, shown in Figure 1.
The most diagnostic carbon atoms found in the 13C NMR spectra
of compounds 1–18 are the ring carbon atoms, which are directly
bonded to a hydroxyl group. There is only one such carbon per
phenol ring, and this carbon is often referred to as the ‘ipso’ carbon.
The ipso carbon atoms in 2,40-dihydroxydiphenylmethane (7) are
C-2 and C-40. The chemical shifts of ipso carbon atoms are found
in the 13C NMR spectra of phenolic compounds between 150 and
160 ppm. The second most diagnostic kind of carbon atom found
in the 13C NMR spectra of 1–18 are the bridge methylene carbon
All five methylol derivatives (2–6) of 4,40-dihydroxydiphenyl-
methane (1) were prepared by the reaction of 1 with excess
°
formaldehyde and base at 60 C for 1 h. Each compound was isolated
by preparative TLC on silica gel. The 1H and 13C NMR assignments
of compounds 1–6 are given in Table 1. It should be emphasized that
all of the 1H and 13C NMR chemical shift values reported here are
specific for the NMR solvent acetone-d6. Chemical shift values from
other NMR solvents cannot be used in our correlation, as discussed
previously.9 A recent study15 found both acetone-d6 and DMSO-d6
Table 1. 13C and (1H, J, Hz) chemical shift values (ppm) for 4,40-dihydroxydiphenylmethanes 1–6 in acetone-d6 solvent
C or (H)
1a
2
3
4
5
6a
133.42
1
2
133.71
133.68
133.70
133.40
133.44
130.45 (7.01, d,
8.1)
130.45 (7.08, d,
2.1)
128.06 (6.97, s)
127.39 (6.97, s)
127.42 (6.97, s)
127.48 (6.97, s)
3
115.93 (6.74, d,
8.1)
128.70
128.79
127.74
127.60
127.60
4
5
156.36
154.38
154.35
152.82
127.74
152.74
127.68
152.73
127.60
115.93 (6.74, d,
8.1)
115.94 (6.71, d,
8.1)
115.87 (6.73, d, 8.4)
6
130.45 (7.01, d,
8.1)
128.07 (6.92, dd,
2.1, 8.1)
128.87 (7.01, d, 8.4)
127.39 (6.93, s)
127.42 (6.97, s)
127.48 (6.97, s)
10
20
133.71
133.73
133.70
133.73
133.62
128b (7.10, d, 2.1)
133.42
130.45 (7.01, d,
8.1)
128.98 (7.03, d,
8.4)
128.06 (6.97, s)
130.46 (7.08, d, 8.1)
127.48 (6.97, s)
30
115.93 (6.74, d,
8.1)
115.94 (6.73, d,
8.4)
128.79
115.94 (6.71, d, 8.1)
128.10
127.60
40
50
156.36
156.42
154.35
156.42
154.25
152.73
127.60
115.93 (6.74, d,
8.1)
115.94 (6.73, d,
8.4)
115.87 (6.73, d, 8.4)
115.94 (6.71, d, 8.1)
115.85 (6.71, d,
8.1)
60
130.45 (7.01, d,
8.1)
128.98 (7.03, d,
8.4)
128.87 (7.01)
130.46 (7.08, d, 8.1)
128b (6.92, dd,
2.1, 8.1)
127.48 (6.97, s)
ArCH2Ar
40.72 (3.76)
40.90 (3.76, s)
61.99 (4.69, s)
41.07 (3.77, s)
61.95 (4.69, s)
41.00 (3.76, s)
41.15 (3.75, s)
62.18 #3,5 (4.71,
s, #3,5) 61.73 # 30
(4.67, s, #30)
128.62 128.94
41.09 (3.74, s)
62.12 (4.71, s)
ArCH2OH
62.28 #3,5 (4.72, s, #3,5)
Unassigned
a See Ref. 9.
b See unassigned peaks at bottom of table.
Copyright  2002 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2002; 40: 747–751

749
Spectral Assignments and Reference Data
Copyright  2002 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2002; 40: 747–751

750
Spectral Assignments and Reference Data
156.4
OH
154.3
OH
152.8
OH
62.2
61.9
62.2
HOCH2
CH2OH
CH2OH
A
C
B
41.0
CH2
CH2
CH2
41.0
41.0
64.3
64.6
HOCH2
64.0
64.7
HOCH2
CH2OH
CH2OH
D
F
E
G
154.7
OH
155.0
OH
153.9
155.7
OH
OH
35.3
CH2
CH2
CH2
CH2
35.3
35.3
35.3
Figure 2. Methylol-substituted phenolic ring types, A–G, found in 2,40- and 4,40-dihydroxydiphenylmethanes. Ipso 13C chemical shifts shown above
OH groups, methylene 13C chemical shift shown to left of CH2 groups and methylol 13C chemical shift shown above CH2OH groups.
The bridge methylene chemical shift values have been used4,8,9
A
B
C
as the easiest way to evaluate the amount and type of diphenyl-
methanes present in the various stages of cure found in PF
resins. A methylene between two 4-hydroxyphenyl rings comes at
40.97 š 0.14 ppm, a methylene between a 4-hydroxyphenyl ring and
a 2-hydroxyphenyl ring comes at 35.32 š 0.14 ppm, and a methy-
lene between two 2-hydroxyphenyl rings comes at 30.5 ppm in
acetone-d6.
D
E F
G
158
157
156
155
154
153
152
TMP
The methylol methylene chemical shift data from 60 to 65 ppm
in acetone-d6 solvent can by used in a diagnostic manner. If there
is a methylol carbon peak in this region that is less than 63.0 ppm,
then this methylol is on a 4-hydroxyphenyl ring. If a peak in this
region is greater than 63.0 ppm, then it represents a methylol group
on a 2-hydroxyphenyl ring. If there is no peak in the 60 to 65 ppm
region but there is a peak near 35 ppm or 41 ppm, then there is
an unsubstituted 2-hydroxyphenyl- or 4-hydroxyphenyl-containing
compound respectively in the resin mixture. This correlation also
holds for trimeric and oligomeric PF methylolarylmethane deriva-
tives.
1
4
5
9
3
7 2
8'
8
6
δ (ppm)
Figure 3. Ipso 13C chemical shift ranges A–G for diarylmethanes (top),
and for methylolphenols (bottom) using compound numbers from
Ref. 9.
atoms, Ar–CH2 –Ar, which bond the two phenol rings together.
Such aryl-connecting methylene carbon atoms are found in 13C
NMR spectra in the region 30–41 ppm. The methylene carbon atoms
of methylol groups, Ar–CH2 –OH, can also give further diagnostic
information about the ring types A–G. The methylol methylene
carbon atoms in 1–18 are found in their 13C NMR spectra between
60 and 65 ppm.
Using the 13C NMR data presented here, it is now possible to
evaluate the chemical components in extracted prepreg PF resins.
This information is also being used to evaluate cured PF resins using
solid-state 13C NMR.
Acknowledgements
A summary of the 13C NMR chemical shift values of the
ipso, bridge methylene, and methylol methylene carbon atoms on
methylolphenolic ring types A–G is given in Fig. 2.
The authors acknowledge support for this research from
NASA/MSFC and Hercules Aerospace Company. We also like to
thank the Mississippi Magnetic Resonance Facility at Mississippi
State University for use of GE-QE 300 NMR.
The 13C chemical shifts of ipso carbon atoms of methylolphenols
were discussed in our previous work.9 Here, we add to that list
the 13C chemical shifts of the ipso carbon atoms of methylol
derivatives of 2,40- and 4,40-dihydroxydiphenylmethanes given in
Tables 1 and 2. Ipso ring carbon types A, B, and C are found
in both 2,40- and 4,40-dihydroxydiphenylmethanes, since each
contains at least one 4-hydroxyphenyl ring. The presence of one
ortho-methylol group causes a 4-ipso carbon to be shielding by
2.1 ppm; the addition of a second ortho-methylol group causes an
additional 1.5 ppm upfield shift. The effects of methylol substituents
on the 13C chemical shifts of the ipso carbon atoms in 2-
hydroxyphenyl ring types D–G are in the same direction, but of
a smaller magnitude.
REFERENCES
1. Knop A, Pilato LA. Phenolic Resins—Chemistry, Applications and
Performance. Springer-Verlag: Berlin, 1985.
2. Freeman JH, Lewis CW. J. Am. Chem. Soc. 1954; 76: 2080.
3. Eapen KC, Yeddanapalli LM. Makromol. Chem. 1968; 119: 4.
4. Francis DJ, Yeddanapalli LM. Makromol. Chem. 1968; 119: 17.
5. Kim MG, Amos LW, Barnes EE. Ind. Eng. Chem. Res. 1990; 29:
2033.
6. Grenier-Loustalot MF, Larroque S, Grenier P, Bedel D. Polymer
1996; 37: 939.
7. Grenier-Loustalot MF, Larroque S, Grenier P, Bedel D. Polymer
1996; 37: 955.
The ipso 13C chemical shift region for phenolic ring types A–G
are shown in Fig. 3 above the chemical shift scale. The ipso chemical
shifts of the methylolphenols studied earlier9 are also given in Fig. 3
below the chemical shift scale. Figure 3 can be used to assign the
ipso region of various stages of cure found in PF resins up to and
including the prepreg stage.
8. Pasch H, Goetzky P, Grundemann E, Raubach H. Acta Polym.
1981; 32: 14.
Copyright  2002 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2002; 40: 747–751

751
Spectral Assignments and Reference Data
9. Fisher TH, Chao P, Upton CG, Day AJ. Magn. Reson. Chem. 1995;
33: 717.
10. Carpenter AT, Hunter RF. J. Appl. Chem. 1951; 1: 217.
11. Maciel GE, Chuang I-S, Gollob L. Macromolecules 1984; 17: 1081.
12. Holopainen T, Alvila L, Rainio J, Pakkanen TT. J. Appl. Polym.
Sci. 1997; 66: 1183.
13. Werster DD. Polymer 1986; 27: 750.
14. Mechen B, Hanton D, Goff JL, Tanneur JP. Eur. Polym. J. 1984; 20:
333.
15. Luukko P, Alvila L, Holopainen T, Rainio J, Pakkanen TT.
J. Appl. Polym. Sci. 1998; 69: 1805.
Copyright  2002 John Wiley & Sons, Ltd.
Magn. Reson. Chem. 2002; 40: 747–751