Org. Synth. 1967, 47, 96
DOI: 10.15227/orgsyn.047.0096
OCTANAL
Submitted by Volker Franzen
1
Checked by Claibourne Smith and V. Boekelheide.
1. Procedure
To a solution of 30 g. (0.4 mole) of anhydrous trimethylamine oxide (Note 1) in 100 ml. of dry chloroform placed in a 250-ml. three-necked, round-bottomed flask fitted with a reflux condenser, a stirrer, and a dropping funnel with protection against moisture is added 48.0 g. (0.2 mole) of n-octyl iodide (Note 2) dropwise with stirring. At the beginning of the addition the flask is warmed to 40–50° on a steam bath to initiate the reaction. The start of the reaction can be recognized by the evolution of heat, and the rate of addition can then be adjusted to maintain the temperature around 50°. Overall the addition requires about 20–30 minutes. When addition is complete, the solution is boiled under reflux for another 20 minutes. Then the solution is cooled, and 110 ml. of 2N aqueous sulfuric acid solution is added with stirring. The chloroform layer is separated and washed successively with water, 2N aqueous sodium carbonate solution, and again with water. After the chloroform solution has been dried over sodium sulfate, it is concentrated under reduced pressure, and then the residue is distilled. The first distillation (Note 3) is carried out at atmospheric pressure and gives 12.0–12.5 g. of a crude oil, b.p. 155–165°. Redistillation using a simple Vigreux column gives 10.6–11.0 g. (41.5–43%) of a colorless oil, b.p. 69–71° (19 mm.), n26D 1.4167.
2. Notes
1.
Trimethylamine oxide is normally available as a hydrate, and for the present preparation it is necessary to convert it to its anhydrous form. A convenient way of doing this is as follows. A solution of
45.0 g. of trimethylamine oxide dihydrate (supplied by Beacon Chemicals) is dissolved in
300 ml. of warm dimethyl-formamide and placed in a three-necked flask set up for distillation. At atmospheric pressure the flask is heated and solvent distilled off until the boiling point reaches
152–153°. Then the pressure is reduced using a
water aspirator, and the remainder of the solvent is distilled. At the end of the distillation the temperature of the bath is slowly raised to 120°. The residual anhydrous
trimethylamine oxide (30 g.) can be dissolved in
100 ml. of chloroform and may remain in the same flask for use in the present preparation.
2.
In place of
n-octyl iodide other derivatives such as
n-octyl bromide,
n-octyl p-toluenesulfonate, and
n-octyl chlorosulfonate can be substituted; the submitter reports that the yields of
octanal in these cases are comparable.
3.
At this stage the product is a waxy semisolid, presumably a trimer or polymer of
octanal, and the higher temperature of an atmospheric distillation is needed to generate the monomeric
octanal.
3. Discussion
Octanal has been prepared by the reduction of
caprylonitrile with
hydrogen chloride and
stannous chloride,
2 by the passage of a mixture of
caprylic acid and
formic acid over
titanium dioxide3 or
manganous oxide,
4 by dehydrogenation of
1-octanol over
copper,
5 and by oxidation of
1-octanol.
6
4. Merits of the Preparation
The conversion of alkyl halides to aldehydes is a synthetic step of broad utility. Earlier procedures for such conversions involving the use of
dimethyl sulfoxide7 or
pyridine N-oxide8 have worked best with activated alkyl halides, although Kornblum has described a modification of the
dimethyl sulfoxide procedure for use with ordinary aliphatic halides.
9 The present procedure using
trimethylamine oxide avoids some of the complicating side reactions of
pyridine N-oxide and is useful with ordinary aliphatic halides.
10,11
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
sulfuric acid (7664-93-9)
hydrogen chloride (7647-01-0)
chloroform (67-66-3)
sodium carbonate (497-19-8)
n-octyl bromide (111-83-1)
sodium sulfate (7757-82-6)
formic acid (64-18-6)
stannous chloride
copper (7440-50-8)
1-Octanol (111-87-5)
caprylic acid (124-07-2)
n-octyl iodide (629-27-6)
manganous oxide
titanium dioxide
dimethyl-formamide (68-12-2)
dimethyl sulfoxide (67-68-5)
Pyridine N-oxide (694-59-7)
OCTANAL (124-13-0)
trimethylamine oxide (1184-78-7)
trimethylamine oxide dihydrate (62637-93-8)
caprylonitrile (124-12-9)
n-octyl p-toluenesulfonate (3386-35-4)
n-octyl chlorosulfonate
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