Preparation of 4-halobenzyl alcohols

The invention provides a process for the preparation of a 4-halobenzyl alcohol of the formula ##STR1## where R.sup.1 is hydrogen, C.sub.1 - to C.sub.20 -alkyl, C.sub.2 - to C.sub.20 -alkoxyalkyl, C.sub.3 - to C.sub.20 -cycloalkyl, or C.sub.4 - to C.sub.30 -cycloalkylalkyl, PA0 R.sup.2 is C.sub.1 - to C.sub.20 -alkyl, C.sub.2 - to C.sub.20 -alkoxyalkyl, C.sub.3 - to C.sub.20 -cycloalkyl or C.sub.4 - to C.sub.30 -cycloalkylalkyl, PA0 X is halogen and PA0 m is 0 to 2, by reacting a haloaromatic carbonyl compound of the formula ##STR2## where R.sup.1, R.sup.2, X and m are as defined above, with hydrogen on a hydrogenation catalyst consisting essentially of copper oxide (I), copper oxide (II) and mixtures thereof in the presence of at least one primary, secondary or tertiary amine selected from the group consisting of acyclic, cyclic and heterocyclic aliphatic amines, in the presence or absence of an inert solvent, at from 50.degree. to 130.degree. C. and at from 10 to 200 bar.

The present invention relates to a process for the preparation of 
4-halobenzyl alcohols by catalytic hydrogenation of haloaromatic carbonyl 
compounds in the presence of copper oxide catalysts. 
The catalytic hydrogenation of haloaromatic carbonyl compounds in the 
presence of copper chromite catalysts is disclosed in DE-A-16 43 876 and 
U.S. Pat. No. 3,527,817. Hydrogenation of ortho-chlorophenyl ketones or 
mixtures thereof with meta- or para-chlorinated isomers or with 
dichlorinated compounds on copper chromite catalysts at higher 
temperatures than in the case of halogen-free compounds to give the 
corresponding carbinols only proceeds at an acceptable rate if alkaline 
earth metal hydroxides are present. The presence of other basic compounds 
alone has no effect, or even an inhibiting effect, on the hydrogenation. 
Only addition of amines having a pKa of at least 3.7 in addition to the 
alkaline earth metal hydroxides accelerates the hydrogenation of 
ortho-chlorophenyl ketones. 
The process described in DE-A-16 43 876 has the following disadvantages: 
The hydrogenation is carried out at temperatures which are higher than in 
the case of halogen-free carbonyl compounds, namely at from 100.degree. to 
175.degree. C., preferably above 150.degree. C.; 
the addition of amines is only possible in combination with alkaline earth 
metal hydroxides; 
the catalysts contain chromium; 
the use of alkaline earth metal hydroxide causes considerable problems for 
continuous hydrogenation since the fact that the alkaline earth metal 
hydroxides are only sparingly soluble or insoluble in the reaction medium 
means that a process of this type cannot be introduced industrially, and 
furthermore deposits cause rapid deactivation of the catalysts (short 
catalyst life). 
It is an object of the present invention to overcome the abovementioned 
disadvantages. 
We have found that this object is achieved by a novel and improved process 
for the preparation of 4-halobenzyl alcohols of the formula I 
##STR3## 
where R.sup.1 is hydrogen, C.sub.1 - to C.sub.20 -alkyl, C.sub.2 - to 
C.sub.20 -alkoxyalkyl, C.sub.3 - to C.sub.20 -cycloalkyl, or C.sub.4 - to 
C.sub.30 -cycloalkylalkyl, 
R.sup.2 is C.sub.1 - to C.sub.20 -alkyl, C.sub.2 - to C.sub.20 
-alkoxyalkyl, C.sub.3 - to C.sub.20 -cycloalkyl or C.sub.4 - to C.sub.30 
-cycloalkylalkyl, 
X is halogen and 
m is 0 to 2, 
which comprises reacting haloaromatic carbonyl compounds of the formula II 
##STR4## 
where R.sup.1, R.sup.2, X and m are as defined above, with hydrogen in the 
presence of an amine on copper catalysts, in the presence or absence of an 
inert solvent, at from 50.degree. to 130.degree. C. and at from 10 to 200 
bar. 
The process according to the invention can be carried out as follows: 
The haloaromatic carbonyl compound II can be reacted with hydrogen at from 
50.degree. to 130.degree. C., preferably from 70.degree. to 100.degree. 
C., under autogenous pressure or by injection of hydrogen, ie. at from 10 
to 200 bar, preferably at from 50 to 150 bar, on a copper catalyst in the 
presence of an amine and in the presence or absence of an inert solvent. 
The hydrogenation can be carried out batchwise or preferably continuously 
in the liquid phase or gas phase, in tubular or stirred reactors, either 
with upward or downward flow through catalysts in suspension, preferably 
in a fixed bed, at a weight hourly space velocity at from 0.05 to 1 kg of 
feed mixture/(kg of catalyst per hour), preferably at from 0.05 to 0.3 kg 
of feed mixture/(kg of catalyst per hour). 
Suitable copper catalysts are those whose catalytically active material 
comprises from 70 to 100% by weight, preferably from 85 to 100% by weight, 
in particular from 95 to 100% by weight, of copper oxide and which contain 
essentially no chromium oxide. The copper oxide catalysts may contain from 
0 to 30% by weight, preferably from 0 to 15% by weight, particularly 
preferably from 0 to 5% by weight, of catalytically active material. 
Suitable copper oxides are copper(I) oxide and copper(II) oxide and 
mixtures thereof. The copper catalysts can be employed as unsupported 
catalysts or preferably on inert support materials, such as aluminum 
oxide, silica, titanium oxide, zirconium oxide, magnesium silicate or 
oxides of the elements from main groups three and four. 
The feed mixture may contain, for example, from 40 to 80% by weight of a 
haloaromatic carbonyl compound II, from 15 to 55% by weight of an inert 
solvent and from 1 to 10% by weight of an amine. The amount of amine added 
should in general be not less than 1% by weight, based on the haloaromatic 
carbonyl compound II, i.e. from 1 to 10% by weight, preferably 1.5 to 5% 
by weight. 
The haloaromatic carbonyl compound II can preferably be reacted dissolved 
in an inert solvent. Suitable inert solvents are ethers, e.g. 
tetrahydrofuran, dioxane, dibutyl ether, dipropyl ether and diethyl ether, 
inert hydrocarbons, such as toluene and xylene, but preferably alcohols, 
such as C.sub.1 - to C.sub.20 -alkanols, preferably C.sub.1 - to C.sub.8 
-alkanols, such as methanol, ethanol, n-propanol, i-propanol and 
n-butanol, particularly preferably ethanol. 
Suitable amines are primary, secondary and tertiary, acyclic, cyclic and 
heterocyclic amines, such as C.sub.1 - to C.sub.20 -alkylamines, eg. 
methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, 
triethylamine, propylamine, dipropylamine, tripropylamine, butylamine, 
dibutylamine, tributylamine, pentylamine, dipentylamine, hexylamine, 
heptylamine, octylamine, nonylamine, decylamine and dodecylamine, 
preferably triethylamine, diethylamine, hexadecylamine and octadecylamine, 
C.sub.1 - to C.sub.20 -monoalkanolamines, eg. dimethyl (hydroxyethyl) 
amine and methyl(hydroxyethyl)amine, C.sub.2 - to C.sub.20 
-dialkanolamines, e.g. methylbis(hydroxyethyl)amine, and heterocyclic 
amines, e.g. pyridine, morpholine, quinoline, piperidine, piperazine and 
derivatives thereof containing one to five C.sub.1 - to C.sub.8 -alkyl 
groups, preferably containing one to three C.sub.1 - to C.sub.4 -alkyl 
groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, 
sec-butyl and tert-butyl. It is also possible to employ mixtures of 
various of the abovementioned amines. 
The process according to the invention for the hydrogenation of 
haloaromatic carbonyl compounds proceeds under significantly milder 
reaction conditions on chromium-free copper oxide catalysts. Furthermore, 
if an amine is added as base, the hydrogenation proceeds without the use 
of solid reaction additives which are industrially impracticable, such as 
inorganic bases, e.g. alkali metal hydroxides and alkaline earth metal 
hydroxides, which result in heterogeneous reaction mixtures. 
During the novel hydrogenation of, for example, p-chloroacetophenone under 
pressure in the presence of from 2 to 10% by weight of an amine and from 
15 to 55% by weight of ethanol as solvent, no deactivation of the copper 
oxide catalysts had occurred after an operating time of more than 900 
hours. 
The reaction products can be separated from the added amine and the solvent 
by distillation, and both the amine and the solvent can be fed back into 
the hydrogenation. The haloaromatic carbonyl compounds II are known from 
Houben-Weyl, Methoden der organischen Chemie, vol. 7/2a, pp. 39ff, and can 
be prepared by the processes described therein. 
R.sup.1, R.sup.2, X and m are defined as follows: 
R.sup.1 and R.sup.2 - independently of one another are 
C.sub.1 - to C.sub.20 -alkyl, preferably C.sub.1 - to C.sub.12 -alkyl, such 
as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, 
tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 
1,2-dimethylpropyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, 
n-octyl, isooctyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, 
isoundecyl, n-dodecyl and isododecyl, particularly preferably C.sub.1 - to 
C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 
isobutyl, sec-butyl or tert-butyl, 
C.sub.2 - to C.sub.20 -alkoxyalky, preferably C.sub.2 - to C.sub.8 
-alkoxyalkyl, such as methoxymethyl, ethoxymethyl,n-propoxymethyl, 
isopropoxy-methyl, n-butoxymethyl, isobutoxymethyl, sec-butoxymethyl, 
tert-butoxymethyl, 1-methoxyethyl or 2-methoxyethyl, 
C.sub.1 - to C.sub.20 -cycloalkyl, preferably C.sub.3 - to C.sub.8 
-cycloalkyl, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, 
cycloheptyl or cyclooctyl, particularly preferably cyclopentyl, cyclohexyl 
or cyclo-octyl, 
C.sub.4 - to C.sub.30 -cycloalkylalkyl, preferably C.sub.4 -to C.sub.20 
-cycloalkylalkyl, such as cyclopentylmethyl, 
R.sup.1 is additionally hydrogen, 
x is halogen, such as fluorine, chlorine, bromine or iodine, preferably 
chlorine or bromine, particularly preferably chlorine, 
m is an integer from 0 to 2, such as 0, 1 or 2, particularly preferably 0 
or 1, 
R.sup.3,R.sup.4 and R.sup.5 are hydrogen, 
C.sub.1 - to C.sub.20 -alkyl, preferably C.sub.1 - to C.sub.12 -alkyl, such 
as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, 
tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 
1,2-dimethylpropyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, 
n-octyl, isooctyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, 
isoundecyl, n-dodecyl or isododecyl, particularly preferably C.sub.1 - to 
C.sub.4 -alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, 
isobutyl, sec-butyl or tert-butyl, 
at least one of the radicals R.sup.3, R.sup.4 and R.sup.5 being different 
from hydrogen. 
The 4-halobenzyl alcohols I are intermediates in the preparation of 
substituted styrenes (U.S. Pat. No. 3,927,133, Org. Synthesis Collective 
Volume 3, 204-206).

EXAMPLES 
EXAMPLE 1 
A solution of 65% by weight of 4-chloroacetophenone, 30% by weight of 
ethanol and 5% by weight of triethylamine was reacted in a tubular reactor 
on a copper oxide/aluminum oxide catalyst (45/55; 3 mm pellets) at a 
weight hourly space velocity of 0.16 kg/(kg of catalyst per hour) at 
90.degree. C. and a hydrogen pressure of bar. After an operating time of 
900 hours under constant experimental conditions, the conversion is 99% at 
a selectivity of 99% (GC area %). 
EXAMPLE 2 
A solution of 63% by weight of 4-chloroacetophenone, 30% by weight of 
ethanol and 2% by weight of diethylamine was reacted in a tubular reactor 
on a copper oxide/aluminum oxide catalyst (45/55; 3 mm pellets) at a 
weight hourly space velocity of 0.16 kg/(kg of catalyst per hour) at 
90.degree. C. and a hydrogen pressure of 100 bar. After an operating time 
of 68 hours under constant experimental conditions, the conversion is 98% 
at a selectivity of &gt;99% (GC area %). 
EXAMPLE 3 
As for Example 2, but with n-butylamine in place of diethylamine. After an 
operating time of 20 hours under constant experimental conditions, the 
conversion is 69% at a selectivity of 80% (GC area %). 
EXAMPLE 4 
A solution of 62% by weight of 4-chloroacetophenone, 25% by weight of 
methanol and 3% by weight of triethylamine was reacted in a tubular 
reactor on a copper oxide/aluminum oxide catalyst (45/55; 3 mm pellets) at 
a weight hourly space velocity of 0.12 kg/(kg of catalyst per hour) at 
120.degree. C. and a hydrogen pressure of 100 bar. After an operating time 
of 33 hours under constant experimental conditions, the conversion is 85% 
at a selectivity of 98% (GC area %). 
EXAMPLE 5 
As for Example 4, but with tetrahydrofuran. After an operating time of 24 
hours under constant experimental conditions, the conversion is 77% and 
the selectivity is 99% (GC area %). 
EXAMPLE 6 
A solution of 75% by weight of 4-chloroacetophenone and 25% by weight of 
ethanol was reacted in a tubular reactor on a copper oxide/aluminum oxide 
catalyst (45/55; 3 mm pellets) at a weight hourly space velocity of 0.12 
kg/(kg of catalyst per hour) at 90.degree. C. and a hydrogen pressure of 
100 bar. After an operating time of 48 hours under constant experimental 
conditions, the conversion is 54% at a selectivity of &gt;99% (GC area %). 
EXAMPLE 7 
A solution of 97% by weight of 4-chloroacetophenone and 3% by weight of 
triethylamine was reacted in a tubular reactor on a copper oxide/aluminum 
oxide catalyst (45/55; 3 mm pellets) at a weight hourly space velocity of 
0.12 kg/(kg of catalyst per hour) at 120.degree. C. and a hydrogen 
pressure of 100 bar. After an operating time of 39 hours under constant 
experimental conditions, the conversion is 58% at a selectivity of &gt;99% 
(GC area %). 
EXAMPLE 8 
A solution of 30% by weight of 4-chlorobenzaldehyde, 68% by weight of 
ethanol and 2% by weight of triethylamine was reacted in a tubular reactor 
on a copper oxide/aluminum oxide catalyst (45/55; 3 mm pellets) at a 
weight hourly space velocity of 0.16 kg/(kg of catalyst per hour) at 
90.degree. C. and a hydrogen pressure of 100 bar. After an operating time 
of 26 hours under constant experimental conditions, the conversion is 97% 
at a selectivity of &gt;99% (GC area %).