Comparative study on reducing aromatic aldehydes by using ammonia borane and lithium amidoborane as reducing reagents

Article abstract of DOI:10.1039/c2nj40227k

Lithium amidoborane (LiNH₂BH₃) and ammonia borane (NH₃BH₃) reduce aromatic aldehydes in tetrahydrofuran (THF) through two different pathways. LiNH₂BH₃ only transfers hydridic hydrogen on boron to aldehydes through a hydroboration process to achieve lithium aminoborate; ammonia borane, on the other hand, transfers both protic and hydridic hydrogens on N and B, respectively, to aldehydes to directly achieve corresponding alcohols. Mechanistic investigations confirm that protic H(N) and hydridic H(B) of ammonia borane participate in the reduction, in which the dissociation of both B-H and N-H bonds is likely to be involved in the rate-determining step. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012.

Full text of DOI:10.1039/c2nj40227k

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PAPER
Comparative study on reducing aromatic aldehydes by using ammonia
borane and lithium amidoborane as reducing reagentsw
Weiliang Xu,a Hongjun Fan,b Guotao Wuc and Ping Chen*c
Received (in Montpellier, France) 23rd March 2012, Accepted 12th April 2012
DOI: 10.1039/c2nj40227k
Lithium amidoborane (LiNH2BH3) and ammonia borane (NH3BH3) reduce aromatic aldehydes
in tetrahydrofuran (THF) through two different pathways. LiNH2BH3 only transfers hydridic
hydrogen on boron to aldehydes through a hydroboration process to achieve lithium
aminoborate; ammonia borane, on the other hand, transfers both protic and hydridic hydrogens
on N and B, respectively, to aldehydes to directly achieve corresponding alcohols. Mechanistic
investigations confirm that protic H(N) and hydridic H(B) of ammonia borane participate in the
reduction, in which the dissociation of both B–H and N–H bonds is likely to be involved in the
rate-determining step.
reduction process was not taken into consideration. Recently,
Menard and Stephan reported that NH3BH3 reduces CO2 to
´
Introduction
Ammonia borane (NH3BH3) and lithium amidoborane
(LiNH2BH3) have been intensively investigated as two promising
solid-state hydrogen storage materials in the past few years.1
NH3BH3 releases the first equiv. of H2 at ca. 110 1C through the
dissociation of both B–H and N–H bonds.1b With the assistance
of additives or catalysts, the dehydrogenation can occur at lower
temperature.2 On the other hand, LiNH2BH3, the product
obtained by substituting one of the protic hydrogens of NH3BH3
by lithium, can release hydrogen at ca. 90 1C in solid state or at
40 1C in tetrahydrofuran (THF) solution.3 Owing to their high
hydrogen content, NH3BH3 and LiNH2BH3 are also reducing
reagents in organic synthesis. In the 1980’s, NH3BH3 was
reported to be a hydride reagent for converting aldehydes or
ketones to alcohols in protic or aprotic solvents.4 Hutchins
and co-workers also reported that NH3BH3 was able to
reduce 4-substitituted cyclohexyl imines, iminium salts and
enamines.5 In addition, LiNH2BH3 was reported to provide
nucleophilic hydride in the reduction of tertiary amide to
primary alcohol in 1996.6
methanol with the assistance of an Al-based frustrated Lewis
pair.7 Theoretical investigations from Zimmerman et al. showed
that NH3BH3 could reduce CO2 through a double hydrogen
transfer process.8 Subsequently, Manner et al. reported that
NH3BH3 can reduce the NQB double bond through this kind
of process.9 Berke and co-workers10 also reported that NH3BH3
reduces imine through a concerted double hydrogen transfer
process, where the protic H(N) and hydridic H(B) are transferred
to the nitrogen and carbon ends of the imine group, respectively
(Scheme 1(a)). Subsequently, a step-wise double hydrogen
transfer mechanism was identified by the same group in the
reaction of NH3BH3 and polarized olefins11 (Scheme 1(b)). In
the case of reduction of ketones and aldehydes by NH3BH3,
however, a different process was proposed, i.e., the dissociation
of ammonia from NH3BH3 occurs before the hydroboration
step due to which a broad signal is observed in the 1H NMR at
0.4 ppm which belongs to free ammonia (Scheme 1(c)) during
However, in those previous studies, NH3BH3 and LiNH2BH3
were both treated as amine borane reagents which only transfer
hydridic H on boron to unsaturated functional groups. The
participation of protic H(N) of NH3BH3 or LiNH2BH3 in the
a Department of Chemistry, National University of Singapore,
Singapore, 117542, Singapore
b State Key Laboratory of Molecular Reaction Dynamics,
Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
Dalian, China 116023
c Dalian National Laboratory for Clean Energy, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian,
China 116023. E-mail: pchen@dicp.ac.cn;
Fax: +86 411-84685940; Tel: +86 411-84379905
w Electronic supplementary information (ESI) available. See DOI:
10.1039/c2nj40227k
Scheme 1 Proposed mechanisms for reducing (a) imines, (b) polarized
olefins, and (c) carbonyl compounds by using NH3BH3.10–12
c
1496 New J. Chem., 2012, 36, 1496–1501
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the reaction of NH3BH3 and ketones.12 Therefore, the protic
H(N)s on NH3BH3 do not participate in this specific
reduction. The products obtained are borate esters based on
the 11B NMR observation. Although detailed mechanism
studies by using benzophenone as representative were given,
the deduction that reduction of aldehydes follows the same reaction
procedure is questionable since the authors did not mention the
observation of free ammonia in the reaction of NH3BH3 and
aldehydes. However, in our research, we found that reduction of
aldehydes by NH3BH3 takes place through a different route where
a double hydrogen transfer process is the main path involved.
Interestingly, reduction of aromatic aldehydes by LiNH2BH3, on
the other hand, follows the hydroboration mechanism.
Fig. 2 (a) 1H NMR characterization of NH3BD3–benzaldehyde
in THF-d8. Singlet at 2.9 ppm attributed to O–H was observed;
(b) 2H NMR characterization for ND3BH3–benzaldehyde in THF.
Singlet at 3.4 ppm attributed to O–D was observed.
Results and discussion
In situ FT-IR and NMR techniques were employed to monitor
the reduction of NH3BH3 and benzaldehyde in anhydrous
THF. It is interesting to find that the intensity of CQO stretch
(at 1705 cmÀ1) decreases while the intensity of O–H stretch
(at 3438 cmÀ1) increases with the progression of reduction
from the in situ FT-IR measurement shown in Fig. 1. It should
be noted that THF is an aprotic solvent. Therefore, the protic
hydrogen which was transferred to the oxygen end of the
carbonyl group must be from NH3BH3, not from solvent.
Since the three Hs bonding with N of NH3BH3 are protic, this
finding indicates that NH3BH3 transferred both protic and
hydridic hydrogens to the carbonyl group.
Table 1 Reactions of NH3BH3 and aldehydes in THFa
Entry
1
Substrate
t/min
Yieldb
76
15
2
3
15
15
87
80
To confirm this, NH3BD3 was employed to react with
benzaldehyde in THF-d8. From the 1H NMR characterization
(shown in Fig. 2(a)), a broad peak at 2.8 ppm attributed to
O–H is observed. This finding confirms the participation of
N–H in the reduction and the formation of O–H. However,
free ammonia at 0.4 ppm which was observed in Berke’s
4
5
15
80
15
15
89
94
12
investigation on reduction of ketones by NH3BH3 does not
appear in the spectrum. Moreover, a deuterated product at the
carbon end of the CQO was obtained with the isolated yield of
79%, which evidences the transfer of deuterium on B of
NH3BD3 to the carbon end of carbonyl group in the reduction
(1H and 13C NMR spectra of the product, a-deuterobenzene-
methanol, are shown in ESIw). In a related experiment of
reacting ND3BH3 and benzaldehyde in THF, a singlet at
6
a
The ratio of substrate and NH3BH3 is 1 : 1, and the concentration of
b
NH3BH3 (or substrate) is 0.2 M. Isolated overall yields.
2
d = 3.4 ppm attributed to O–D was observed by H NMR
that the main path for the reduction is via the double hydrogen
transfer process, in which both H(N) and H(B) of NH3BH3
participate in the reaction and transfer to the O and C sites of
carbonyl group, respectively (Scheme 2).
(the spectrum can be seen in Fig. 2(b)). Free ND3 was also
absent. All these isotopic labeling experimental results together
with the high yield of phenylmethanol (entry 1, Table 1) confirm
Borate ester, a key species in the mechanistic interpretation,12
was also observed in our in situ 11B NMR characterization (Fig. 3).
However, it is a minor by-product which is too little to be isolated
from the solution for quantification. The majority of B species is,
Fig. 1 In situ FT-IR measurements of the reaction between 0.005 M
NH3BH3 and 0.005 M benzaldehyde. The changes in intensities of
OH stretch vibration at 3438 cmÀ1 (a) and CQO stretch vibration at
1705 cmÀ1 (b) were monitored with time.
Scheme 2 The reaction process of NH3BH3 reducing benzaldehyde:
NH3BH3 transfers protic Ha to oxygen end of carbonyl and hydridic
Hb to carbon end of carbonyl.
c
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Fig. 3 In situ 11B NMR characterization of reacting NH3BH3 with
one equiv. of benzaldehyde at room temperature. A small broad peak
at 19.0 ppm, which belongs to borate ester, was observed. The quartet
at À22.0 ppm is attributed to un-reacted NH3BH3.
on the other hand, precipitated from the reacting solution upon
reduction, forming a white amorphous substance. The solute is,
however, mainly composed of an alcohol product and un-reacted
NH3BH3 or benzaldehyde. We, therefore, tentatively ascribe
the formation of minor borate ester to the alcoholysis between
ammonia borane and phenylmethanol.
Based on the results mentioned above, various aromatic
aldehydes were chosen to react with NH3BH3. The results are
shown in Table 1. The ratio of the substrate and NH3BH3 was
1 : 1. All the reactions were carried out in 15 min at room
temperature (detected by GC). The isolated overall yields of
corresponding primary alcohols are in between 76 and 94%.
Similar to NH3BH3, LiNH2BH3 also has protic H(N) and
hydridic H(B) and may exhibit similar performance in
reduction of aldehydes. However, to our surprise, a white
precipitate was formed when benzaldehyde reacted with
LiNH2BH3 in THF, and no phenylmethanol was detected by
GC. On the other hand, high isolated yield of phenylmethanol
can only be achieved after hydrolyzing the precipitate by
aqueous HCl. In order to determine the composition of the
white precipitate, we collected the sample of LiNH2BH3 with
3 equiv. of benzaldehyde for Raman and NMR characterizations.
From the Raman spectrum shown in Fig. 4(a) we can find that
B–H stretching vibrations in the range of 2140–2360 cmÀ1
disappear. However, N–H vibrations are still observable at
3168 and 3210 cmÀ1. Additionally, only one singlet signal at
2.0 ppm was observed by 11B solid NMR as shown in
Fig. 4(b). It is, therefore, very likely that the precipitate is
lithium aminotribenzylborate of formula a (Scheme 3). The
composition of a was further confirmed by 1H NMR and
13C NMR. However, the molecular weight cannot be determined
due to the instability of the borate compound in GC-MS.12
Similar reactions were observed in the reduction of other
aldehydes with LiNH2BH3. The results are shown in Table 2.
The ratio of the substrate and LiNH2BH3 is 1 : 1. All aldehydes
reacted rapidly with LiNH2BH3 to afford 100% conversion
rate in 5 min at room temperature. The high isolated overall
yields of corresponding primary alcohols were only achieved
after hydrolysis of the borate ester in aqueous HCl solution.
Moreover, LiND2BH3 was also used to react with benzaldehyde
in THF. During the reaction, a white precipitate was formed and
deuterated benzenemethanol, PhCH2OD, was not observed by
GC-MS. In a similar reaction, after hydrolyzing the white
precipitate from the reaction of LiNH2BD3 and benzaldehyde,
a-deuterobenzenemethanol (PhCHDOH) was obtained with
an isolated yield of 82%. Clearly, reduction of aldehydes by
Fig. 4 (a) Raman spectra for LiNH2BH3 (above) and white precipitate
(below). The NH2 vibrations in LiNH2BH3 at 3306 and 3364 cmÀ1 shift
to 3168 and 3210 cmÀ1 in white precipitate. (b) 11B solid NMR
spectrum for white precipitate. Singlet at 2.0 ppm is observed.
Scheme 3 The process of reduction of benzaldehyde by LiNH2BH3.
Table 2 Reactions of LiNH2BH3 and aldehydes in THFa
Yieldb (%) w/t Yieldc (%) after
Entry Substrate
1
t/min hydrolysis
hydrolysis
5
5
N.A.
N.A.
85
2
3
4
91
93
91
5
5
N.A.
N.A.
5
5
5
N.A.
N.A.
88
91
6
a
The ratio of substrate and LiNH2BH3 is 1 : 1, and the concentration
b
c
of LiNH2BH3 (or substrate) is 0.167 M. Detected by GC. Isolated
overall yields.
c
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Table 3 Initial rates of formation of [OH] at different concentrations
of NH3BH3 and benzaldehyde
and 2.85 (kNH BH /kNH BD )
3
for NH3BD3–benzaldehyde.
3
3
3
Because those DKIE values are greater than 2 and close to
each other, the dissociation of both N–H and B–H bonds is
likely to be involved in the rate-determining step.22
Initial rate of
[OH]/M minÀ1
Entry
[NH3BH3]/M
[Benzaldehyde]/M
1
2
3
0.0083
0.0166
0.0083
0.025
0.025
0.050
0.0011
0.0020
0.0020
Conclusions
In conclusion, NH3BH3 is an efficient reagent in reducing
aromatic aldehydes. In situ FT-IR and NMR measurements
evidence that the reduction is through double hydrogen transfer
process, which is significantly different from the hydroboration
mechanism proposed in previous investigations. LiNH2BH3 is
also a powerful reagent in reducing aromatic aldehydes.
However, in contrast to NH3BH3, LiNH2BH3 cannot transfer
its protic hydrogen to aldehydes. The overall reduction process
is identical to the hydroboration of aldehydes by NaBH4. High
yields of corresponding alcohols are achieved only after the
hydrolysis step.
LiNH2BH3 resembles the hydroboration of aldehyde by
NaBH4.13 Both reagents only transfer hydridic H(B) to aldehydes.
One possible explanation for the difference between LiNH2BH3
and NH3BH3 in reducing aldehydes is that the N–H bond
distance (0.96 A3a) in LiNH2BH3 is shorter than that in NH3BH3
(1.07 A14). It makes the transfer of the protic hydrogen from
LiNH2BH3 to the carbonyl group difficult.
The direct reduction of aldehydes to alcohols by NH3BH3
should be the consequence of dissociation of both B–H and
N–H bonds followed by the addition of Hs to CQO, which
resembles the double hydrogen transfer (DHT) hydrogenation
of carbonyl compounds, which is via a dihydride route catalyzed
by transition metals15 or Meerwein–Ponndorf–Verley (MPV)
reduction.16 Ru,17 Ir,18 Rh19 and aluminum alkoxides complexes20
are effective catalysts for this process.
Experimental section
General remarks
Solvents and most of reagents were purchased commercially
and used without further purification: THF (J&K, HPLC, dried
over NaH), benzaldehyde (Sigma-Aldrich, 99%), 4-methyl-
benzaldehyde (Alfa Aesar, 98%), 4-methoxybenzaldehyde
(J&K, 99%), 4-chlorobenzaldehyde (Acros, 99%), 4-nitro-
benzaldehyde (J&K, 99%), methyl 4-formylbenzoate (Alfa, 98%),
ammonia borane (Sigma-Aldrich, 97%), LiH (Alfa, 98%).
ND3BH3 and NH3BD3 were synthesized according to Penner’s
work.23 NMR spectra were recorded on a Bruker DRX-500
instrument. Chemical shifts, quoted in ppm, are relative to the
In order to further understand the reaction mechanism,
detailed kinetic studies and computational simulations were
carried out. Kinetic studies of the reaction of NH3BH3 and
benzaldehyde were investigated in THF at room temperature
by employing kinetic and quantitative FT-IR measurements.21
Determination of reaction order is based on the initial
formation rate of [OH] under different concentrations of
NH3BH3 and benzaldehyde. The results (Table 3) show that
the reaction obeys a second-order rate law, being first order to
[NH3BH3] and [benzaldehyde] respectively. According to the
plot of 1/[benzaldehyde] versus time (Fig. 5(a)), the rate law at
room temperature can be expressed as in eqn (1)
2
internal or external standard (only for H NMR and 11B NMR):
1
singlet d = 0 ppm of TMS for H NMR; the middle of CDCl3
triplet d = 77 ppm for 13C NMR; singlet d = 4.80 ppm of
D2O for 2H NMR; singlet d = 0 ppm of BF3ÁEt2O for
11B NMR. IR spectra were recorded on a Varian 3100
FT-IR spectrophotometer using Resolution Pro program.
GC results were detected by RAMIN 2060 series. The model
of capillary column was HP-5. MS analyses were performed
on Agilent 6890-5973 GC-MS. Raman spectra were recorded on
a Renishaw Raman microscope.
n = 5.62[NH3BH3][benzaldehyde]
(1)
Deuterium kinetic isotopic effects (DKIE) were analyzed to
further understand the reaction process. Plots of 1/[benzaldehyde]
versus time (t) based on the results of kinetic in situ FT-IR
measurements of the reactions of benzaldehyde with NH3BH3,
ND3BH3 or NH3BD3 are shown in Fig. 5, respectively. The DKIE
value is 3.47 (kNH BH /kND BH ) for ND3BH3–benzaldehyde
Synthesis of LiNH2BH3
3
3
3
3
1 mmol NH3BH3 was firstly dissolved in 5 ml THF in a metal
jar in a glove box. Then, 1 mmol LiH was quickly added into
the solution and the jar cap was closed. The system was stirred
at room temperature. After one equivalent of H2 was released,
as detected by a pressure gauge, clear 0.2 M LiNH2BH3
solution was obtained characterized by 11B NMR. The
solution can be directly used in reduction reaction without
further purification.
General experimental procedure for reducing aldehydes with
NH3BH3
4 ml of 0.25 M NH3BH3 THF solution was added into 1 ml of
1 M aldehyde solution in THF in a closed glass bottle at room
temperature. An FT-IR spectrometer was employed to monitor
Fig. 5 1/[benzaldehyde] versus time plots for 0.005 M benzaldehyde
reacting with 0.005 M NH3BH3 (a), 0.005 M NH3BD3 (b), 0.005 M
ND3BH3 (c), respectively.
c
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the consumption of the carbonyl group and formation of the
OH group. After the reaction, THF was evaporated, and then
10 ml hexane was added into the glass bottle to extract alcohol
product three times. Then, clear hexane solution was collected
after centrifugation. Next, hexane was evaporated and a
transparent liquid residue was left. In the end, further column
chromatography (silica gel, 200–300 mesh, elution by using
ethyl acetate : hexane = 1 : 10 solution) was utilized to purify
4-Methoxylphenylmethanol (entry 3, Table 1). 1H NMR
(500 MHz, CDCl3, 25 1C; TMS): d = 2.2 (s, 1H; O–H), 3.8
(s, 3H; CH3), 4.6 (s, 2H; CH2), 6.8–6.9 (m, 2H; ArH), 7.2–7.3
ppm (m, 2H; ArH); 13C NMR (126 MHz, CDCl3, 25 1C;
CDCl3): d = 55.3, 64.9, 113.9, 128.6, 133.2, 159.2 ppm; FT-IR
(film): nmax = 3354, 3032, 3001, 2935, 2836, 1612, 1514, 1247,
1033, 816 cmÀ1; MS (EI): m/z (%) 138 [M]+ (100), 109 (73),
121 (52), 77 (50), 94 (33).
1
the alcohol product. Alcohol was characterized by H NMR,
13C NMR, FT-IR and MS.
4-Chlorophenylmethanol (entry 4, Table 1). 1H NMR
(500 MHz, CDCl3, 25 1C; TMS): d = 2.1 (s, 1H; O–H), 4.6
(s, 2H; CH2), 7.2–7.3 ppm (m, 4H; ArH); 13C NMR
(126 MHz, CDCl3, 25 1C; CHCl3): d = 64.5, 128.3, 128.7,
133.3, 139.3 ppm; FT-IR (film): nmax = 3342, 2953, 2920,
2855, 2731, 1597, 1491, 1450, 1405, 1086, 1012, 708 cmÀ1; MS
(EI): m/z (%) 142 [M]+ (60), 77 (100), 107 (68), 113 (18).
General experimental procedure for reducing aldehydes with
LiNH2BH3
5 ml of 0.2 M LiNH2BH3 THF solution was added into 1 ml of
1 M aldehyde solution in THF in a closed glass bottle at room
temperature. An FT-IR spectrometer was employed to monitor
the consumption of the carbonyl group. The formation of a
white precipitate was observed during the reaction. After the
reaction, THF was evaporated, and then 5 ml of 2 M HCl
aqueous solution was added into the glass bottle. The system was
stirred at room temperature for 30 min. Next, the solution was
extracted with 10 ml diethyl ether three times. The combined
diethyl ether extracts were washed with brine, dried with NaSO4
overnight and concentrated in vacuum. In the final step, the
residue was purified by silica gel flash chromatography to obtain
the desired product. The product was characterized by FT-IR,
1H NMR, 13C NMR and GC-MS.
4-Nitrophenylmethanol (entry 5, Table 1). 1H NMR
(500 MHz, CDCl3, 25 1C; TMS): d = 2.2 (s, 1H; O–H), 4.8
3
(s, 2H; CH2), 7.5 (d, JHH = 8.86 Hz, 2H; ArH), 8.2 ppm
(d, 3JHH = 8.76 Hz, 2H; ArH); 13C NMR (126 MHz, CDCl3,
25 1C; CDCl3): d = 64.0, 123.7, 127.0, 147.3, 148.3 ppm;
FT-IR (film): nmax = 3521, 3112, 2924, 2884, 1602, 1511, 1344,
1196, 1057, 736 cmÀ1; MS (EI): m/z (%) 153 [M]+ (34), 77
(100), 107 (50), 89 (41), 51 (28), 136 (22).
Methyl 4-(hydroxymethyl)benzoate (entry 6, Table 1).
1H NMR (500 MHz, CDCl3, 25 1C; TMS): d = 2.1 (s, 1H;
O–H), 3.9 (s, 3H; CH3), 4.7 (s, 2H; CH2), 7.4–7.5 (m, 2H;
ArH), 8.0–8.1 ppm (m, 2H; ArH); 13C NMR (126 MHz,
CDCl3, 25 1C; CDCl3): d = 52.0, 64.6, 126.4, 129.3, 129.8,
145.9, 166.9 ppm; FT-IR (film): nmax = 3384, 3032, 3001,
2935, 2836, 1710, 1612, 816 cmÀ1; MS (EI): m/z (%) 166 [M]+
(40), 77 (100), 107 (60), 136 (30).
Product characterization
a-Deuterobenzenemethanol. 1H NMR (500 MHz, CDCl3,
3
25 1C; TMS): d = 2.2 (s, 1H; O–H), 4.6 (d, JHH = 9.90 Hz,
2H; CH2), 7.3–7.4 ppm (m, 5H; ArH); 13C NMR (126 MHz,
CDCl3, 25 1C; CDCl3): d = 64.9 (t, JCD = 21.84 Hz), 127.0,
127.6, 128.5, 140.8 ppm; FT-IR (film): nmax = 3338, 3087,
3064, 3030, 2915, 2135, 1496, 1453, 1208, 1201, 734, 697 cmÀ1
MS (EI): m/z (%) 109 [M]+ (80), 79 (100), 92 (20).
;
Notes and references
1 (a) A. Staubitz, A. P. M. Robertson and I. Manners, Chem. Rev.,
2010, 110, 4079–4124; (b) F. H. Stephens, V. Pons and R. T. Baker,
Dalton Trans., 2007, 2613–2626.
Lithium aminotribenzylborate (a, Scheme 3). 1H NMR
(500 MHz, DMSO-d6, 25 1C; TMS): d = 3.3 (s, 2H; N–H),
4.4–4.5 (m, 6H; CH2), 7.1–7.3 ppm (m, 15H; ArH); 13C NMR
(126 MHz, DMSO-d6, 25 1C; DMSO-d6): d = 63.4, 125.7,
126.8, 127.8, 128.4 ppm.
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Phenylmethanol (entry 1, Table 1). 1H NMR (500 MHz,
CDCl3, 25 1C; TMS): d = 2.8 (s, 1H; O–H), 4.6 (s, 2H; CH2),
7.3–7.4 ppm (m, 5H; ArH); 13C NMR (126 MHz, CDCl3,
25 1C; CDCl3): d = 65.0, 126.9, 127.4, 128.4, 140.8 ppm;
FT-IR (film): nmax = 3335 (O–H), 3087, 3064, 3030, 2931,
2873, 1496, 1453, 1208, 1201, 734, 697 cmÀ1; MS (EI): m/z (%)
108 [M]+ (94), 79 (100), 51 (19), 91 (16).
4-Methylphenylmethanol (entry 2, Table 1). 1H NMR
(500 MHz, CDCl3, 25 1C; TMS): d = 1.9 (s, 1H; O–H), 2.4
(s, 3H; CH3), 4.6 (s, 2H; CH2), 7.2 (d, JHH = 7.89 Hz, 2H;
3
3
ArH), 7.3 ppm (d, JHH = 8.08 Hz, 2H; ArH); 13C NMR
(126 MHz, CDCl3, 25 1C; CDCl3): d = 21.2, 65.2, 127.1,
129.2, 137.7, 137.4 ppm; FT-IR (film): nmax = 3334, 3048,
3021, 2950, 2919, 1518, 1445, 1032, and 802 cmÀ1; MS (EI):
m/z (%) 122 [M]+ (92), 107 (100), 91 (69), 79 (65).
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