Preparation of the chloromethylene dibenzoate
Methylene dibenzoate is easily obtained from trioxymethylene and benzoic anhydride by the Wegscheider and Späth method in the presence of a few drops
of concentrated sulfuric acid and could be converted into a monochlorinated product in the following manner.
60 g of methylene dibenzoate were dissolved in benzene and treated with chlorine, which had been passed through a wash bottle with sulfuric acid and a
tower with calcium chloride for drying, until a weight gain of 9 g was achieved. After distilling off the benzene, the chlorinated product
crystallised on cooling and was recrystallised from acetone or petroleum ether for purification. In its crystalline form and in its solubility
behaviour, it shows the greatest similarity to unchlorinated methylene dibenzoate. There is also only a difference of two degrees in the melting
point, as it melts at 96, while methylene dibenzoate has a melting point of 98. However, a mixed melting point of the two substances resulted in a
depression of a few degrees. The analysis led to the following results:
I. 0.1966 g of substance yielded 0.1058 g of silver chloride.
II. 0.1973 g of substance yielded 0.1102 g of silver chloride.
III. 0.3058 g of substance yielded 0.6969 g of carbonic acid and 0.1131 g of water.
[Table of composition: parts by elements in 100 parts of substance]
In order to prove that the chlorine atom had actually entered the methylene group, the chlorine product was saponified [hydrolized?] with alcoholic
[caustic] potash. If the hydrogen atom of the methylene had been replaced by chlorine, the chlorine product had to be split into benzoic acid and
formic acid, whereas if substitution had occurred in the ring, it had to yield chlorobenzoic acid and formaldehyde on decomposition.
For the qualitative detection of the decomposition products, 5 g of chloromethylene dibenzoate was dissolved in 4 g of [caustic] potash in alcohol and
boiled for 4 hours under reflux. The excess [caustic] potash was then precipitated as carbonate by introducing carbonic acid, filtered off and the
filtrate evaporated to dryness. The residue was taken up with a small amount of water and filled with hydrochloric acid. The precipitated substance
had a melting point of 121 and was therefore benzoic acid. The filtrate of this reduced mercuric chloride by causing a white precipitate that turned
black with ammonia, thus it was calomel.
The chlorination therefore proceeded according to the equation:CH2(OCOC6H5)2 + Cl2 =
CHCl(OCOC6H5)2 + HCl
In addition, the formation of formic acid could also be monitored quantitatively using the method of Vortmann and Skala.
5.1734 g chloromethylene dibenzoate was boiled with 5 g of [caustic] potash in 60 cm3 alcohol for 4 hours, then, as described earlier, the
main quantity of benzoic acid was removed, the filtrate etherified [ether added?], the free acid removed from the ethereal solution by shaking with
sodium hydroxide solution and the sodium formate solution obtained evaporated. The residue was taken up with water, neutralised with a few drops of
pure [glacial?] acetic acid and mixed with mercuric chloride. The precipitated mercuric chloride was dried on a tared filter at 100 degrees, weighed
and its weight was 0.8223 g, whereas 0.8177 g was theoretically required. |
but it appears that the chlorination is carried
out under ambient conditions in benzene, which should probably be replaced by something safer.