[COl.TllIUUTION FROM
THE
CHEMrSTRY DEPARTMENT, CSIVERSITY O F CALIFORSIA,
LOS
akNC;EI.ES]
The Photolysis of Chloroacetone at 3 130 A. BY
A. N.
STR.ICHAN AND
F.E. BLACET
RECEIVED ~ I A 31, Y 1955 The vapor pliase photochemical decomposition of chloroacetone a t wave length 3130 8. has been studied over the temperature range 59 t o 335'. The principal products identified mass spectrometrically are hydrogen chloride, acetone, acetonylacetone and s>-mmetricalbiacetylethylene. The quantum yields of hydrogen chloride and acetone increase, while those of tlie remaining t ~ decrease o with increasing temperature. A t the higher temperatures, carbon monoxide, metliarie and nicth:\.i chloride are also formed. The effects of nitric oside and of iodine on the photolysis have also been studied. In the presence of nitric oxide, the quantum yield of hydrogen chloride is increased slightly t o a value close t o unity while the yields of acetone and acetonylacetone become negligible and there is evidence t h a t the nitroso compound, C H 3 C O C H 2 S 0 ,is formed. \i,.ith iodine vapor present, iodoacetone is formed and acetonylacetone is again eliminated. The yield of hydrogen chloride is greatly reduced. The investigation indicates t h a t the main primary process is CH3COCH2C1 h y = CH3COCH2 f CI. The postulation of disproportionation as well as association of acetonyl radicals is necessary to explain the rcsults. The activation energl- for the abstraction of a hydrogen atom from chloroacetone by a n acetonyl radical has been found t o be 9 2~ 1 kcal./mole assuming zero activation energy for the association of acetonyl radicals.
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Pressures tvere measured with a calihrated click gage reproducible to better than 0.5 mm. For each run a small quantity of chloroacetone \vas removed from the storage bulb and degassed thrce times a t - 78". I t TT'LLS allowed to fill the cell t o the desired pressure. I n the nitric oxide runs, the chloroacetone introduced ~ v a i condensed with Dry Ice and the cell filled with the desired pressure of S O . In the iodine runs, the chloroacetone was condensed in a trap outside the cell. Iodine was admitted Experimental to the cell and its pressure measured. Finally, both the Eastman Kodak Company chloroacetone was dissolved iodine and chloroacetone \rere condensed inside the cell with in water and shaken repeatedly with small aliquots of ethyl liquid nitrogen. In both the iodine a n d nitric oside runs, ether. This procedure preferentially removes the main mixing was achieved by diffu5ion over 2 two-hour period impurity, unsymmetrical dichloroacetone. The chloro- prior t o the run. At the end of the nitric oxide runs, the acetone remaining in the water layer was extrwted ri-it11 excess S O was rczmoved a t - 196" arid discarded, and anal!.ether and distilled at reduced pressure. The center frac- sis for non-condensable products \vas not attempted. 4 t tion was dried over anhydrous calcium chloride and stored the end of the iodine runs, the excess iodine o'as rcinoved a t Dry Ice temperature. M a spectrometric analysis in- by reaction with mercury. All products xverc identified dicated better than 99.9% purit The absorption spectrum and analyzed in ii modified \Yestinghouse, T y p e L\.,in:i\i of chloroacetone vapor in the n r ultraviolet was measured spectrometer. Standardization was effected bb- iritroducon a Cary spectrophotometer a ~ i dextends from 3300 to irig measured samples of pure compounds. Standard Yamples of CO, CH,, CH.,Cl and HCl were measured in ;I 2400 A. with a maximum a t 2900 A . micro-gas buret. In the case of acetone and acetonj-lSitric oside was prepared by the reduction of nitrite by a small quantit!. of the compound was condensed iodide.2 I t was distilled in the vacuum apparatus from acuated tube, weighed and expanded into a cnli- 183 t o - lBii", the center third being retained. Mass brated five-liter volume, to which vas attached a smaller spectrometric analysis indicated that the only possible imcalibrated volume. After equilibrium, the sniallcr volume purity was nitrogen. I t was assumed t h a t this ~ v o u l dnot \vas closed and the amount of the compound contained in it influence the experiments. C . P . iodine was vacuum suhlimed. A center fraction was retained and used. C . P . (21 known fraction of a known 11-eighti introduced into tlie mass spectrometer. :icetone was vacuum distilled with the retention of the center From each run, the following fractions of products wrrc third. hIass spectrometric analysis showed no impurities. analyzed separately. The light source ~ v a ian Hanovia Tl-pe ,4 medium pres( 1 1 The material noli-condensnhle a t - 19ti". sure mercury lami,. A f3irly parallel and uniform light ( 2 ) The fraction which volatilized a t -78". This conbeam was achieved b!- use of a pair of quartznlenseswith :L combined focal length of 5 c m . The 3130 A . filter cotn- sisted of most of the acetone and hydrogeii chloride p l u 5 a little chloroacetone. hination was t h a t described by Soyes and Leighton.3 The potassium hiplithalate solution was circulated to and from ( 3 ) Part of the fraction which volatilized a t -50". T h e :I three-liter reservoir. The transmission of the filter cotnundeconiposed cliloroacetone could be largely removed froin bination was measured on L: Car)- spectrophotometer atid the less \-ohtile products bl- a two-hour fractionation a t -,60°. This portion n-as warmed to 0' and opcnccl to ;i extends from 3100 t o 3400 A . with a maximum a t 3130 A . knowri volume. The vapor which filled tliis volume \\:is A cylindrical quartz cell with plane \vintlo\r\, 20 cni. in lengtli, 3 a n . internal diameter, na-: used. In a l l experi- analyzed. I t consisted of chloroacetone PILI\ most of a n y remaining acetone and hydrogen chloridc. ments, tlie light beam filled the cell. A n aluminuin block ( 4 ) A repetition of ( 3 ) , the known volume being filled ;I housed the cell and was lieatcd electricall)-. \.arkitions of the light intensity were followed b y a phototube (Beck- second timc. ( 5 ) The fraction remaining involatile a t - c50°. Thi5 m a n type 2312-1) mounted behind the cell and recorded on contained the acetonj-lacetone. Esperirnents in \f-liicli a sensitive milliammeter. The phototube, cell, block and known amount5 of ;icetonylacetone were added to chloroconnecting tubing were all enclosed in a n air thermostat acetone indicated t h a t some aceton!-lacctoIie viis curieti maintained a t 60". The rractioii cell w a i connected by stopcocks to the chloroacetone supply and through a series over with the chloroacetone a t -50". .A correction in tlie of traps to the vacuum pumps and a Toepler pump. -4 yields of acetonylacetone to :illow for thiq h a s been applied. DrJ- Ice trap virtuall)- excluded mercury from the %>.stein, Runs 14 and 15 are the onl)- ones in lvliich this correction amounts to more than 20' ( . For these two runs, tlic q u a n t I ) This work was supported in part bi- t h e Otlice
