THE C A T A L Y T I C S Y N T H E S I S OF H E X A C H L O R O B U T A D I E N E

V. A. N e k r a s o v a a n d N. I. S h u i k i n

N. D. Zelinskii Institute of Organic Chemistry, Academy of Sciences, USSR

Tramlated from Izvestiya Akademii Nauk SSSR, Otdelenie Khimicheskikh Nauk, No. a, pp. 496-498, March, 1962

Original article submitted October 26, 1961

There is very l imited information in the literature on the question of perpartng hexachlorobutadiene. McBee

and Hatton [1] synthesized hexachlorobutadiene without using a catalyst. The authors heated polychlorbutadiene to

high temperature at atmospheric pressure. They thus obtained hexachlorobutadiene with a high yield, and small a-

mounts of carbon tetrachloride, ethylene tetrachloride, and hexachloroethane which were mixed with the product of

the main reaction. The authors did not indicate the temperature of the reaction for formation of the hexachlorobu-

tadiene. Shostakovskii, Shapiro, and Shmolina [2] worked out a method for chlorination of diacetylene in carbon tet- rachloride at low temperatures, from -30 to-9.5*. The resulting 1,1,2,3,4,4-hexachloro-2-butene was chlorinated in

a glass ampoule with ultraviolet i l luminat ion to formation of octachlorobutane. By treatment of the latter with aque- ous alcoholic alkali they obtained hexachlorobutadiene with a yield of 6'/0]0.

In the present work we have carried out the catalyt ic dehydrochlorination ,of polychlorobutanes (1,1,2,3,4,4- hexachlorobutane and 1,1,1,2,3,4,4,4-octachlorobutane) to obtain hexachlorobutadiene by the scheme

CHC]2-- CHC1 - - CHC1 - - CHCI2 + 2CI~ -+ CC12 = CCI - - CCI = CCI~ + 4HCI (1) CC18 - - CHCI - - CHCI - - CCln ~ CCIz = CCI - - CCI = CC12 -t- 2HCI (2)

Preliminary experiments showed that the optimum temperature for formation of hexachlorobutadiene was 470- 475*, after which all the main experiments were carried out at this temperature. The catalysts had a very important

effect on this reaction. We found that a suitable and available catalyst which assured a high yield was Crimean co-

quina. About the same results were also obtained using infusorial earth.

E X P E R I M E N T A L

The starting polychlorobutanes were prepared catalyt ical ly [3] or by photochemical chlorination of a technical

mixture of tetrachlor0butanes which boiled in the range 190-200" and had d~ ~ 1.3844. Pot rapid chlorination of the

chlorobutane fraction with maximum use of chlorine, the experiments were carried out in an apparatus for careful

dispersion of the gases [4]. The reaction vessel was heated to 140" and i l luminated with a lamp (200 W) at a dis- tance of 12 cm. During chlorination of the chlorobutane fraction (which was controlled by determination of the sp.

gr.) the chlorination temperature was gradually raised to 180, 190, 200, and 210". The chlorinated product had d~ ~ 1.6901, boiled in the range 205-9.12", and was taken as a mixture of hexa- and octachlorobutanes. The first series

of experiments on dehydrochlorination of the polychtorobutanes into hexachlorobutadiene was carried out in a stream

of chlorine at 476* and a volume rate 0.17 hour "1. The rate of passing the chlorine was 1.3 liters/hour. The poly-

chlorobutanes were introduced into an iron tube filled with iron turnings from a special buret which assure$t even heating. The catalyt ic tube was placed in an electric oven with an automatic temperature regulator controlled by an iron-constantan thermoeouple. The reaction products were passed into a receiver cooled with ice and salt, and the gaseous portion was passed into a graduated gasometer. The yield of hexachlorobutadiene in this case did not ex- ceed 37~ We then studied the action on the dehydrochlorination reaction of the following catalysts: coquina, in- fusorial earth, and a mixed catalyst consisting of CrzO s + AlzC h + MgO (45 : 30 : 25 mole 0]0). Best results were ob- tained when the reaction was carried out in the presence of Crimean coquina. This catalyst was prepared in the fol- lowing way: the coquina was ground in a mortar, sifted through a sieve with pore size 0.25 mm and ignited in a porcelain crucible for three hours in a muffle oven at white heat; after cooling we added a small amount of distilled

water to form a thick mass which was then pressed. The resulting cakes (thickness about 1 cm) were dried, broken

into pieces with a size of 3-4 ram, and dried at 200* to constant weight. Pull removal of water from the catalyst, as is known, increases its activity. When moisture was present in the catalyst there was a change in its macrostructure with enlargement of the micel lar aggregates and the micropores almost disappeared, so that the catalyst lost act iv-

468

Dehydrochlorinat ion of Polychlorobutanes

Yield of Unreacted Yield of Residue in Catalyst ca t a lyza te , g polychlorobutane, % hexachlorobutadiene, % flask, % Loss, %

Coquina

Infusorial earth

Cr=O s, AI~O s, MgO

25.4

24.7

18.5

25.3

26.4

35.3

57.2

55.3

35.3

15.3

16.2

19.7

2.2

2.1

9.7

ity,[5]. The processes of movement of moisture in a porous body are complex, the more so in that we must consider the presence in the moisture of at least two phases (liquid and vapor). The situation is stil l more compl ica ted if the moisture which fills the pores is a solution of any substance (for example , meta l chlorides [6]). Therefore, for m a x i - mum removal of moisture the cata lys t was heated to 470* and dry air was passed over it to full disappearance of wa- ter vapor in the receiver. The cata lys t from infusorial earth was prepared in the same way as the coquina, The mixed ca ta lys t was prepared by simultaneous precipi ta t ion of the me ta l hydroxides from solution of the corresponding nitrates with a solution of potassium hydroxide and subsequent t rea tment with hydrogen. The results of the second seri,es of exper iments are given in the table. In each exper iment we took 26.5 g of the polychlorobutane mixture. It

follows from the results given in the table that the most ac t ive ca ta lys t for dehydrochlorination is ignited coquina. We also carried out experiments in which, under standard conditions, we used ignited coquina as the cata lys t

but introduced nitrogen along with chlorine in the react ion tube. The rate of passing the chlorine and nitrogen was the same, 1.3 l i ters/hour. This showed that the nitrogen had a positive effect on the degree of dehydrochlorination,

since the yield of hexachlorobutadiene rose to 66-68%. As an example we give the constants for the separate fractions obtained in the dis t i l la t ion of the chlorinated

products. Fraction I, boi l ing up to 212" (755 ram) had d~ ~ 1.6906, taken for unreacted polychlorobutanes. Fraction II, boi l ing in the range 2.1.4-216" (755 ram) with d~ ~ 1.6823 and n~ 1.5545, was hexachlorobutadiene. Fract ion III was a crysta l l ine residue in the flask. Analysis of fraction Ih Pound: C 18.26; C1 81.73%. C4C16. Calcu la ted : C 18.39; CI 81,61%.

S U M M A R Y

1. We have found a suitable and ava i lab le cata lys t for preparing hexachlorobutadiene. 2. Dilution of chlorine with nitrogen in the rat io I : 1 has a favorable effect on the degree of dchydrochlor ina-

t ion of polychlorobutanes.

L I T E R A T U R E C I T E D

1. E . T . McBee and R. E. Hatton, Industr. and Engng. Chem. 41, 809 (1949). 2. M.F . Shostakovskii, E.S. Shapiro, and L. I. Shmolina, Dokl. AN SSSR 118, 114 (1958). 3. V . A . Nekrasova, VIII Mendeleev Congress, Section of Organic Chemistry and Technology [in Russian], 101 (1959). 4. V . A . Nekrasova, Zh. Obshch. Khimii 28, 1557 (1958). 5. I .E . Neimark, L. Kh. Freidlin, A. I. Rastrenko, and N. V. Borunova, Izv. AN SSSR. Otd. Khim. n. 1956, 784. 6. V . A . Nekrasova, ,Khim. Nauka i Prom-st ' 4, 408 (1959).

All a b b r e v i a t i o n s of p e r i o d i c a l s in the a b o v e b i b l i o g r a p h y are l e t t e r - b y - l e t t e r t r a n s l i t e r -

a t i o n s o f the a b b r e v i a t i o n s as g iven in the o r ig in a l R u s s i a n journal . Some or all o f th i s per i -

od i ca l literature may well be available in English translation. A complete list of the cover-to. c o v e r E n g l i s h t r a n s l a t i o n s appears st the back o f th i s i s s u e .

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