Preparation of tertiary alcohols

Tertiary alcohols are prepared by oxidizing tertiary aldehydes with oxygen at elevated temperatures. The tertiary alcohols prepared in this way are valuable and versatile intermediates for dyes, drugs and crop protection agents and are used, for example, in the preparation of agrochemicals.

The present invention relates to a process for the preparation of tertiary 
alcohols by oxidizing tertiary aldehydes with oxygen at elevated 
temperatures. 
In general, tertiary alcohols have hitherto chiefly been prepared either 
from olefins by adding water, or from carbonyl compounds, for example 
ketones or esters, by reacting them with organometallic compounds. 
Tertiary alcohols can also be prepared by hydrolyzing the corresponding 
halides or esters, by reacting epoxides with organometallic compounds or 
by oxidizing saturated compounds with powerful oxidizing agents (Ullmanns 
Encyklopaedie der Technischen Chemie, Volume 3, pages 285 to 288). 
However, a disadvantage of these processes is that some of the starting 
materials are not readily accessible. The processes are also 
unsatisfactory from the point of view of economical and simple operation 
and yield of pure end product, particularly on an industrial scale. 
We have now found that tertiary alcohols of the formula 
##STR1## 
where R.sup.1, R.sup.2 and R.sup.3 are identical or different and each is 
an aliphatic, cycloaliphatic, araliphatic or aromatic radical, are 
obtained in an advantageous manner when tertiary aldehydes of the formula 
##STR2## 
where R.sup.1, R.sup.2 and R.sup.3 have the above meanings, are reacted 
with free oxygen or air at elevated temperatures of about 60.degree. to 
160.degree. C. and in a reaction medium consisting essentially of the 
reaction components. 
If 4-cyano-2,2-dimethylbutyraldehyde is used, the reaction can be 
represented by the following equation: 
##STR3## 
Compared with the prior art, the process according to the invention gives 
tertiary alcohols by a simpler and more economic route and in better yield 
and purity. All of these advantageous results of the invention are 
surprising. Thus, a known reaction of 4,4-dimethyl-4-formyl-butaonic acid 
nitrile with oxygen gives only isocaproic acid (Z. Naturforsch. 5b, 
(1950), 122), and the reaction of 4-cyano-2,2-dimethyl-butyraldehyde with 
oxygen in an aqueous medium containing mineral acid gives 
2,2-dimethylglutaric acid (German Pat. No. 1,618,177). It is also 
generally known that the oxidation of aldehydes with oxygen chiefly gives 
the corresponding carboxylic acids or anhydrides (Houben-Weyl, Methoden 
der Organischen Chemie, Volume 8, page 24). 
Preferred starting materials II and hence preferred end products I are 
those where R.sup.1, R.sup.2 and R.sup.3 are identical or different and 
each is alkyl of 1 to 8 carbon atoms, in particular of 1 to 4 carbon 
atoms, cycloalkyl of 5 to 8 carbon atoms, alkylaryl or arylalkyl of 7 to 
12 carbon or phenyl. These radicals can also be substituted by groups 
and/or atoms which are inert under the reaction conditions, for example 
alkyl or alkoxy of 1 to 4 carbon atoms, chlorine, bromine or cyano, or, if 
desired, the carbon chains in aliphatic R.sup.1, R.sup.2 and R.sup.3 can 
be interruptd by 
##STR4## 
Suitable tertiary aldehydes II are thus acetaldehydes which are substituted 
in the .alpha.-position by 3 identical or different groups chosen from 
methyl, ethyl, propyl, isopropyl, butyl, sec.-butyl, isobutyl, 
tert.-butyl, pentyl, cyclopentyl, cyclohexyl, benzyl or phenyl. Preferred 
starting materials II are 2,2-dimethyl-3-phenyl-propionaldehyde, 
2-benzyl-2-methyl-butyraldehyde, acetoxypivalaldehyde, 
isopropylcarbonyloxypivalaldehyde, 
2-ethyl-2-methyl-3-isopropylcarbonyloxypropionaldehyde, 
4-cyano-2,2-dimethyl-butyraldehyde, 4-cyano-2-methyl-2-propylbutyraldehyde 
and 4-cyano-2,3,3-trimethyl-butyraldehyde. 
Oxygen is used as such, or advantageously in the form of air. The oxidation 
is advantageously carried out with a stoichiometric amount or an excess of 
oxygen, preferably with from 1 to 10, in particular with from 2 to 8, 
moles of oxygen per mole of starting material II. 
The oxidation is advantageously carried out at from 60.degree. to 
160.degree. C., preferably from 70.degree. to 140.degree. C., under 
atmospheric or superatmospheric pressure, batchwise or continuously. It is 
preferably carried out without a catalyst. However, it may sometimes be 
necessary to use a catalyst in order to achieve higher rates of reaction. 
Examples of suitable catalysts are heavy metal salts, for example 
NiCl.sub.2, Ni(OCOCH.sub.3).sub.2, VCl.sub.3, CrCl.sub.3 and CeCl.sub.3, 
and corresponding complex compounds, for example tetraimidazole-Ni(II) 
chloride. The amount of catalyst is not critical and is generally from 
0.01 to 0.1 mole percent of starting material. Whether a catalyst is 
required at all and which catalyst is advantageous can easily be 
determined in each particular case by a preliminary experiment. 
The reaction can be carried out as follows: a mixture of starting material 
II and oxygen, and, if desired, an organic solvent and/or a catalyst is 
kept at the reaction temperature for from 2 to 10 hours. The end product 
is then separated off in the conventional manner, for example by 
fractional distillation. 
The tertiary alcohols prepared in this way are valuable and versatile 
intermediates for dyes, drugs and crop protection agents and are used, for 
example, in the preparation of agrochemicals (Japanese Published 
Application 14446/68). An end product I can thus be reacted, for example, 
in the following way: 
##STR5## 
to give valuable intermediates for herbicides. 
The parts given in the Examples which follow are by weight.

EXAMPLE 1 
80 parts of oxygen are passed into 172 parts of 
isopropylcarbonyloxypivalaldehyde in a stirred reactor at 100.degree. C. 
in the course of 5 hours. When the reaction has ended, the reaction 
mixture is subjected to fractional distillation. 118 parts (74% of theory) 
of 2-hydroxy-1-isopropylcarbonyloxy-2-methylpropane (boiling point 
48.degree.-49.degree. C./0.4 mbar) are obtained. 
EXAMPLE 2 
125 parts of 4-cyano-2,2-dimethyl-butyraldehyde are reacted by a method 
similar to that in Example 1. 89 parts (78% of theory) of 
4-hydroxy-4-methyl-valeronitrile (boiling point 112.degree.-114.degree. 
C./16 mbar) are obtained.