I found this synth many moons ago:
Chloromethylation of Benzene
C6H6 + CH2O + HCl __> C6H5.CH2Cl + H2O
A mixture of 600g (7.7 moles) of C6H6, 60g (2 moles) of paraformaldehyde*, and 60g of pulverized ZnCl2** is heated to 60°C with stirring. While this temp. is maintained, a rapid stream of HCl is passed into the reaction mixture until no more gas is absorbed (~ 20 minutes).
The organic layer is removed, washed with water and then with dilute NaHCO3***, dried over CaCl2, and fractionally distilled. After the excess C6H6 has been removed there is obtained 200g (79%) of Benzyl Chloride, b.p. 70°C (15 mm).
There are also produced about 12g of p-xylylene dichloride, m.p. 100°C, and a small amount of diphenylmethane.
Notes:
* It is possible to use 40% formalin in place of the paraformaldehyde. In this case more ZnCl2 is required. The following proportions are most satisfactory:
400g C6H6, 75g of 40% formalin & 100g ZnCl2
The reaction is carried out as described; if allowed to run 12hrs, a 70% yield of diphenylmethane is obtained.
**If the proportion of ZnCl2 is increased, the yield of dichloromethyl derivative is correspondingly greater; if less is used, almost no dichloromethyl compound is produced but the yield of Benzyl Chloride is diminished.
***It is absolutely necessary to remove all the Zn salt by the washings. Without this precaution the product almost completely resinifies during the distillation period.
Although the reaction usually is carried out with ZnCl2 as the catalyst, H2SO4 and AlCl3 have also been used. These catalysts are sometimes objectionable because they tend to favor the formation of diphenylmethane derivatives.
