F. E. Condon Sokoloff City College of New York
and Murray
I
I I
Photochlorination of Hvdrocarbons with Chlorine Generated in
b
A Student Laboratory Exercise
Fair yields of chlorocyclohexane have been obtained simply and safely by irradiating a heterogeneous mixture of cyclohexane (1 mole), concentrated hydrochloric acid (100 ml), and manganese dioxide (Baker and Adamson, 95% "precipitated," 0.2 mole). Chlorine generated in a lower aqueous layer by the well-known reaction MnOz
+ 4HC1-
MnC12
+ C12 + 2H90
rises into the supernatant hydrocarbon layer where, under the influence of light from a 300-watt incandescent lamp, the substitution reaction takes place: CL
-
+ CGHU
CaHnCI
+ HC1
In adapting the experiment to performance by each individual of a large laboratory group beginning their study of organic chemistry, a simple .apparatus was constructed that permitted irradiation of six reaction flasks a t once. Irradiation time was 8-10 hours, and thirty flasks could be processed in a week. During one laboratory period, each student places the cyclohexane and manganese dioxide in a 500-ml Florence flask fitted with an air-cooled condenser, and leaves i t with the instructor. Addition of hydrochloric acid and irradiation are carried out between laboratory periods by the instructor or supervisor of laboratory work. The
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Journol o f Chemicol Educofion
next laboratory period is devoted to working up the reaction product.' Besides demonstrating a photochemical process and an importaut reaction of hydrocarbons which has preparative value, the exercise provides early practice in typical laboratory techniques and calculations. The choice of cyclohexane because it can give only one monochlorination product is worth pointing out to the students as is the use of an excess of cyclohexane to h i t polysubstitution. In a preliminary investigation of the scope of the chlorination method described, toluene gave benzyl chloride, identified by conversion via the Grignard reagent and phenyl isocyanate to phenylacetanilide. Benzene gave the addition product, hexachlorocyclohexane. Two of the geometrical isomers were isolated by standard procedure^:^ the alpha isomer, mp 155', and the beta isomer, mp 295-300'. From diphenylmethane, we obtained practical yields of benzhydryl chloride, identified by its hydrolysis to benzhydrol, mp 64-65", and dichlorodiphenylmethane, identified by its conversion to benzophenone 2,4dinitrovbenvlhvdrazone. " " A
' A detailed desoription of apparatus and procedure will be furnished upon request. Slade, R.E., Chem. andInd.,1945,31k10.
