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DOI: 10.1055/s-0031-1290595
Base-Catalyzed Direct Transformation of Benzylamines into Benzyl Alcohols
Publication History
Publication Date:
28 February 2012 (online)
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Abstract
Benzylamines were directly transformed into benzyl alcohols in superheated aqueous methanol in the presence of a base catalyst. This process is simple and will provide an alternative industrial route to benzyl alcohols such as xylene glycols.
Key words
alcohols - amines - catalysis - substitution - solid-phase synthesis
- Supporting Information for this article is available online:
- Supporting Information
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After our patent application,¹¹b another patent application¹¹c was published. It was reported that when benzylamine and an equivalent amount of glycolic acid were heated in supercritical methanol, the amide was probably generated in situ, and then it was converted into benzyl alcohol with good yield.
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References and Notes
We examined the reaction of MXG and methylamine as a representative of the reverse reaction, that is, transformation of benzyl alcohols into benzylamines. So far, MXDA was not obtained.
13In order to check metal leaching from the stainless-steel autoclave, ICP analysis of the reaction solution was performed [reaction conditions: MXDA/MeOH/H2O/NaOH = 1:110:70:1.4 (molar ratio), 240 ˚C, 2 h]. The concentrations of Fe, Cr, Ni, and Mo were 0.018, 0.058, 0.0, and 3.0 ppm, respectively. The reaction also conducted in a glass vessel when it was carried out in 1-undecanol under reflux at atmospheric pressure. Therefore, it was considered that metal leaching from the reaction vessel was minute and its effect was marginal.
14MXDA, mono-alcohol, MXG, MeOH, and methylamine were only observed, and no other byproducts or inter-mediates were detected in the time-course GC analysis of the reaction.
15Reactions under N2 and H2 (initial pressure: 1 MPa) were investigated and compared with those at 1 atm N2. Even under H2 pressure, the reaction smoothly proceeded and no differences were observed. Combined with the fact that no byproducts or intermediates were detected, it was thus not considered probable that the reaction proceeded via imine or aldehyde intermediates.
16From the fact that the yields of N-methyl and N,N-dimethyl benzylamine were very low, it was apparent that N-methylation by methanol did not occur during the reaction
17
Preparation of
m
-xylene glycol
(MXG); Typical Procedure (Table 1)
To a 30-mL autoclave
was added MXDA (0.30 g, 2.2 mmol), catalyst (0.1 g), and MeOH (7.4
g), and then the inner gas was replaced by N2. The mixture
was heated at 240 ˚C for 2 h, and then cooled
in an ice-water bath. The yield was determined by GC analysis
using tridecane as internal standard. The crude products were purified
by Kugelrohr distillation.
Spectral data of MXG (Table
[³]
, entry7): ¹H
NMR (500 MHz, CD3OD): δ = 4.60 (s,
4 H), 7.24-7.34 (m, 4 H). ¹³C
NMR (126 MHz, CD3OD): δ = 65.2, 126.6,
126.9, 129.4, 142.8.
Preparation of
benzyl alcohol derivatives (Table 4): To a 30-mL autoclave
was added benzylamine derivative (4.4 mmol for entry 9, 11, and
12, and 2.2 mmol for the others), powdered NaOH (0.1 g, 2.5 mmol),
MeOH (7.4 g), and H2O (2.9 g), then the inner gas was
replaced by N2. The mixture was heated at 240 ˚C
for 2 h, and then cooled in an ice-water bath. The reaction
mixture was neutralized with 1 M HCl (2.5 mL, 2.5 mmol). GC yield
was determined by GC analysis using tetradecane (entry 4) and tridecane
(for the others) as internal standard. For entry 1, the solutions
were dried over Na2SO4, concentrated, and
purified by silica-gel column chromatography (hexane-EtOAc, 75:25
v/v). The other products were purified by Kugelrohr distillation.
Spectral
data of benzyl alcohol (Table
[4]
,
entry1): ¹H NMR (500 MHz, CD3OD): δ = 4.59
(s, 2 H), 7.23-7.33 (m, 5 H). ¹³C
NMR (126 MHz, CD3OD): δ = 65.2, 126.6,
126.9, 129.4, 142.8.
All other
products were characterized by comparison of GC retention time with
chemical reagents purchased from commercial suppliers.