Preparation of m-(p-bromophenoxy)benzaldehyde

A process for preparing m-(p-bromophenoxy)benzaldehyde of the formula, ##STR1## characterized by brominating m-phenoxybenzaldehyde with bromine or bromine chloride as a brominating agent.

The present invention relates to a process for the production of 
m-(p-bromophenoxy)benzaldehyde of the formula, 
##STR2## 
and more particularly it relates to the selective bromination of 
m-phenoxybenzaldehyde. 
In general, the halogenation of aromatic hydrocarbons with a halogen is a 
well-known reaction, but this reaction requires a catalyst in many cases 
and produces isomers as by-product which often make the operation 
troublesome because of the need for their separation. Particularly, an 
industrial, direct halogenation which is carried out without protecting 
highly reactive functional groups such as an aldehyde group, as intended 
in the present invention, has never been established. In many cases, the 
halogenation is carried out after protecting the aldehyde group with 
aluminum chloride or the like. 
As is described in D. E. Pearsons: J. Org. Chem. 23, 1412 (1958), for 
example, it is common that the halogenation of aromatic aldehydes produces 
an acid halide when a catalyst is not used, while it produces a 
nuclear-halogen derivative only when a catalyst such as silver sulfate is 
used. Particularly, from the description in the above literature that the 
use of an equivalent weight or more of aluminum chloride based on 
benzaldehyde is essential to nuclear halogenation, it is easily 
understandable that the process of the present invention is not a common 
reaction and can never be easily analogized. 
Further, in order to demonstrate that the process of the present invention 
is one which makes the most use of the structural characteristics of the 
compound itself, chlorination of the compound was carried out as follows 
in a similar manner to the process of the present invention: Chlorine gas 
was passed through a solution of m-phenoxybenzaldehyde in a solvent. The 
results are shown in Table 1. 
As can be seen from the table, this reaction produces an isomer, 
m-(o-chlorophenoxy)benzaldehyde, as by-product together with large amounts 
of impurities. This tendency is improved to some extent by lowering the 
reaction temperature, but the problems such as low yield of the objective 
compound and formation of m-(o-chlorophenoxy)benzaldehyde as by-product 
still remain unsolved. Particularly, the formation of the by-product, 
m-(o-chlorophenoxy)benzaldehyde, makes it difficult to remove the 
by-product from the objective compound, m-(p-chlorophenoxy)benzaldehyde. 
For example, purification by distillation is very difficult because of the 
similar boiling point of both compounds, and chemical purification with 
sodium hydrogen sulfite can not be an effective means because of almost 
the same behaviour of the both compounds to that chemical. In order to 
improve the position selectivity and yield, the catalytic effect of ferric 
chloride, zinc chloride and titanium chloride was investigated. Good 
results were not however obtained: The pure yield was slightly improved 
but the amount of m-(o-chlorophenoxy)benzaldehyde increased, as is 
apparent from Table 1. Further, solvent effect was also investigated to 
some degree, but chlorobenzene and tetrachloroethylene were inferior to 
methylene chloride in the position selectivity and pure yield. 
From the fact previously found by the inventors that the conventional 
pyrethroid type insecticides having a halogen atom at the p-position show 
a great reduction in toxicity to fishes, the inventors extensively studied 
to obtain m-phenoxybenzaldehyde having a halogen atom at the p-position 
which is a useful intermediate for the production of these pyrethroid type 
insecticides (Kasamatsu et al.: Japanese Patent Application Nos. 
125420/1978, 125421/1978, 85714/1978, 71489/1977 and 69119/1977). As a 
result, it was found unexpectedly that the bromination of 
m-phenoxybenzaldehyde proceeds with an extremely high selectivity and a 
high yield. The inventors thus attained to the present invention. 
m-Phenoxybenzaldehyde used as a starting material in the present invention 
can easily be produced, for example, by the processes disclosed in 
Japanese Patent Application Kokai (Laid-Open) Nos. 143638/1976, 
40732/1978, 82736/1978 and 112824/1978. This compound is already 
commercially available as an intermediate for many pyrethroid type 
insecticides of economical importance and extreme effectiveness. It is 
therefore apparent that the process of the present invention makes it 
possible to produce the objective compound at low cost and with extreme 
ease of operation, high yield and high selectivity as clearly shown in the 
examples, and therefore is far superior to other processes in economy and 
operation. 
In the present invention, the bromination of m-phenoxybenzaldehyde may be 
carried out in the presence or absence of a solvent. However, it is 
preferably carried out in a halogenation-resistant solvent at a 
temperature lower than the boiling point of the solvent, preferably lower 
than room temperature. The solvent includes methylene chloride, 
tetrachloroethylene, chlorobenzene and the like. Catalysts are not 
required at all in general, but the reaction is not hindered even though a 
metal halide such as aluminum chloride, ferric chloride, zinc chloride or 
the like is present in the system. 
The completion of the reaction can easily be determined by the 
gas-chromatographical examination of the disappearance of the material. 
The objective m-(p-bromophenoxy)benzaldehyde can be obtained in a high 
purity and with high yield by merely removing the solvent by evaporation. 
The results of the experimental bromination of m-phenoxybenzaldehyde 
according to the present invention are shown in Table 2. As is apparent 
from the table, the bromination proceeds smoothly without special heating 
even in the absence of a catalyst, and besides it shows an extremely high 
selectivity without being accompanied by m-(o-bromophenoxy)benzaldehyde as 
by-product. 
Neither an increase in the o-isomer nor a remarkable effect on the pure 
yield are observed, unlike the chlorination, even though a metallic salt 
such as ferric chloride, aluminum chloride, zinc chloride or the like is 
present as a catalyst in the system. Further, in the present invention, 
tetrachloroethylene and chlorobenzene may be used as a solvent with the 
same good result as with methylene chloride. 
The bromination of the present invention may be carried out using not only 
a bromine molecule but also bromine chloride as a brominating agent. The 
result is shown in Table 2. 
Bromine chloride has the defect that the pure yield is low as compared with 
the bromine molecule, but it is advantageous in cost and retention of the 
high selectivity. The crude product obtained by these methods can be 
purified into m-(p-bromophenoxy)benzaldehyde of higher purity by 
distillation or the like.

Next, the present invention will be illustrated in more detail with 
reference to the following reference examples and examples. Examples and 
reference examples other than those mentioned below were carried out and 
their results are shown in Tables 1 and 2. 
REFERENCE EXAMPLE 1 
9.90 Grams (0.050 mole) of m-phenoxybenzaldehyde were dissolved in 40 ml of 
methylene chloride, and chlorine gas was passed through the resulting 
solution at 0.degree. C. for 30 minutes. After the reaction was finished, 
the reaction solution was treated in the same manner as in Example 1 (No. 
ii in Table 1). 
Yield: 11.54 g (99.2% of the theoretical amount) 
EXAMPLE 1 
9.90 Grams (0.050 mole) of m-phenoxybenzaldehyde were dissolved in 40 ml of 
methylene chloride, and a solution of 9.60 g (0.060 mole) of bromine in 10 
ml of methylene chloride was added dropwise to the resulting solution at 
0.degree. C. taking a period of 1 hour with stirring. After the addition 
was finished, the reaction was continued for a further 3 hours at the same 
temperature. The reaction solution was washed with water and then with a 
dilute aqueous potassium sulfite solution to decompose bromine in the 
organic layer. The organic layer obtained was washed with a dilute aqueous 
sodium carbonate solution and then a dilute aqueous sodium chloride 
solution followed by drying over anhydrous sodium sulfate and 
concentration. (No. 2 in Table 2). 
Yield: 12.95 g (93.5% of the theoretical amount) 
b.p.: 130.degree.-135.degree. C. (0.12 mmHg) 
EXAMPLE 2 
0.41 Gram (0.0025 mole) of anhydrous ferric chloride was added to a 
solution of 9.90 g (0.050 mole) of m-phenoxybenzaldehyde in 40 ml of 
methylene chloride to obtain a homogeneous solution. Thereafter, a 
solution of 9.60 g (0.060 mole) of bromine in 10 ml of methylene chloride 
was added dropwise to the solution at 0.degree. C. taking a period of 1 
hour with stirring. The reaction solution was then treated in the same 
manner as in Example 1 (No. 3 in Table 2). 
Yield: 12.62 g (91.1% of the theoretical amount) 
EXAMPLE 3 
9.90 Grams (0.050 mole) of m-phenoxybenzaldehyde was dissolved in 40 ml of 
methylene chloride. Separately from this, 4.80 g (0.030 mole) of bromine 
and 1.78 g (0.025 mole of chlorine were reacted at -20.degree. C. in 
methylene chloride to prepare a solution of bromine chloride in mehtylene 
chloride. This solution was added dropwise to the above solution at 
-30.degree. C. taking a period of 30 minutes with stirring. After the 
addition was finished, the reaction was continued for a further 30 minutes 
at the same temperature. The reaction solution was treated in the same 
manner as in Example 1 (No. 8 in Table 2). 
Yield: 13.29 g (96.0% of the theoretical amount) 
EXAMPLE 4 
9.60 Grams (0.060 mole) of bromine were added dropwise to 9.90 g (0.050 
mole) of m-phenoxybenzaldehyde at 0.degree. C. taking a period of 1 hour 
with vigorous stirring. After the addition was finished, the reaction was 
continued for a further 3 hours at the same temperature. The unreacted 
bromine was distilled off under reduced pressure from the reaction system 
to obtain m-(p-bromophenoxy)benzaldehyde (No. 9 in Table 2). 
Yield: 13.14 g (94.9% of the theoretical amount) 
Table 1 
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Catalyst (mole %, 
Unreacted 
m-(o-Chloro- 
m-(p-Chloro- 
based on m- m-phenoxy- 
phenoxy- 
phenoxy- 
Pure 
Tempera 
phenoxybenzalde- benzaldehyde 
benzaldehyde 
benzaldehyde 
yield 
No. ture hyde (%) (%) (%) (%) 
__________________________________________________________________________ 
Methylene 
i -15.degree. C. 
-- chloride 
&lt;0.1 4.5 71.7 68.3 
Methylene 
ii 0.degree. C. 
-- chloride 
&lt;0.1 4.5 65.4 64.9 
Methylene 
iii 20.degree. C. 
-- chloride 
&lt;0.1 3.5 57.4 59.1 
Methylene 
iv -15.degree. C. 
FeCl.sub.3 (5 mole %) 
chloride 
&lt;0.1 8.5 75.7 73.8 
Methylene 
v -15.degree. C. 
FeCl.sub.3 (2.5 mole %) 
chloride 
&lt;0.1 7.7 76.2 72.2 
Methylene 
vi 0.degree. C. 
FeCl.sub.3 (5 mole %) 
chloride 
&lt;0.1 11.2 73.2 70.2 
Methylene 
vii 0.degree. C. 
ZnCl.sub.2 (5 mole %) 
chloride 
&lt;0.1 8.9 73.0 70.1 
Methylene 
viii 
0.degree. C. 
AlCl.sub.3 (5 mole %) 
chloride 
&lt;0.1 8.1 67.3 62.3 
Methylene 
ix -15.degree. C. 
TiCl.sub.4 (5 mole %) 
chloride 
&lt;0.1 5.8 70.6 68.3 
AlCl.sub.3 (equivalent 
Methylene 
x -15.degree. C. 
weight) chloride 
&lt;0.1 17.6 58.2 55.5 
Chloro- 
xi 0.degree. C. 
-- benzene 
&lt;0.1 3.8 48.0 54.2 
Tetrachloro- 
xii -15.degree. C. 
-- ethylene 
&lt;0.1 9.8 61.6 62.5 
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Table 2 
__________________________________________________________________________ 
Catalyst (mole %, 
Unreacted 
m-(o-Bromo- 
m-(p-Bromo- 
based on m- m-phenoxy)- 
phenoxy)- 
phenoxy)- 
pure 
Tempera- 
phenoxybenzal- benzaldehyde 
benzaldehyde 
benzaldehyde 
yield 
No. 
ture dehyde Solvent 
(%) (%) (%) (%) 
__________________________________________________________________________ 
Methylene 
1 20.degree. C. 
-- chloride 
0.1 &lt;0.1 91.4 85.1 
Methylene 
2 0.degree. C. 
-- chloride 
0.1 &lt;0.1 92.8 86.8 
Methylene 
3 0.degree. C. 
FeCl.sub.3 (5 mole %) 
chloride 
0.1 &lt;0.1 92.3 84.1 
Methylene 
4 0.degree. C. 
AlCl.sub.3 (5 mole %) 
chloride 
0.1 &lt;0.1 93.0 87.0 
Methylene 
5 0.degree. C. 
ZnCl.sub.2 (5 mole %) 
chloride 
0.1 &lt;0.1 92.8 85.5 
Tetrachloro- 
6 0.degree. C. 
-- ethylene 
0.1 &lt;0.1 92.5 86.3 
Chloro- 
7 0.degree. C. 
-- benzene 
0.1 &lt;0.1 92.3 86.5 
BrCl (as bromina- 
Methylene 
8 -30.degree. C. 
ting agent) 
chloride 
0.1 &lt;0.1 84.9 81.5 
9 0.degree. C. 
-- -- 0.1 &lt;0.1 88.1 83.6 
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