COMMUNICATIONS SELECTIVE CHLORINATION OF 2,3-DICHLOROPROPENE WITH tert-BUTYL HYPOCHLORITE The conversion of 2,3-dichloropropene into 1,2,3-trichloropropene has been effected in 60% yield by photochemical chlorination, using tert-butyl hypochlorite as the halogenating agent.
THEuse of tert-butyl hypochlorite as a reagent for the free-radical chlorination of hydrocarbons is well established (Carlsson et al., 1966; Caserio and Pratt, 1967; Clarke, 1931; Harford, 1939; Walling, 1957; Walling and Heaton, 1965; Walling et al., 1956; Walling and Jacknow, 1960a,b; Walling and Kurkov, 1966; Walling and Thaler, 1961; Walling and Wagner, 1964). Whereas this ester has a selectivity intermediate between molecular chlorine and bromine for saturated hydrocarbons (Walling and Jacknow, 1960a), it is far more selective than the latter with acetylenic and olefinic substrates (Walling et al., 1956; Walling and Thaler, 1961). The present work was undertaken to extend the scope of this reaction to substrates already containing one or more halogen atoms.
compounds already containing one or more halogen atoms. Where cis-trans isomerism is possible, both isomers would probably be obtained. The observed product distribution may be rationalized in terms of the following mechanism:
Results
The data are summarized in Table I. Figure 1 shows that the yield of 1,2,3-trichloropropene (cis and trans) increased with decreasing hypochlorite-to-olefin ratio. tert.BuOC1
OFELIN
(MOLE R A T I O )
Discussion
Figure 1. Effect of tert-butyl hypochlorite on product distribution for radical chlorination of 2,3-dichloropropene to 1,2,3-trichIoropropene with photochemical initiation at 35" f
The selectivity of tert-butyl hypochlorite toward the further halogenation of 2,3-dichloropropene is such that only one trichlorinated alkene (1,2,3-trichloropropene) was produced. This finding suggests that tertiary alkyl hypohalites in general, and tert-butyl hypochlorite in particular, may provide an effective method of obtaining a single derivative by the chlorination of olefinic and acetylenic
5"c. 0 Neat @ In benzene 8 Incremental addition of terf-BuOCI
Table I. Radical Chlorination of 2,B-Dichloropropene to 1,2,3-TrichIoropropene with fed-Butyl Hypochlorite at 35' f 5' C.
Reaction mixtures irradiated several hours with direct sunlight, 100-watt electric light bulbs, or both. 1,2,3. 1,2,3-Trichloropropene 2,3 or 2,3-CL-P. 2,3-Dichloropropene
Solvent None (neat) Sunlight and
bulb Direct sunlight 100-watt bulb Benzene, 100-watt bulb
2,s
Compn. of Reaction Product, MoleslMole tert-BuOCl 1,2,3 BuOH
tert-BuOCl/ 2,3-Clz-P, Init. M.R."
% ' Yield Based
on tert-BuOCl 1,2,3 Ethe4
N.D.'
0.38
N.D.
0.45:
38
62
N.D. N.D.
0.52 0.61
0.59 0.44
0.11 0.05,
52 61
48
0.38
0.26
0.65
0.78
26
74
39
Initial mole ratio. *Ether by-product identified functionally by infrared. Only one unknown peak appeared on gas-liquid chromatograms, indicating single ether. Only traces of Claaddition products found. No data. tert-BuOCl charged in two increments.
460
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
tert-BuOC1 + hv tert-Bu0.
I[
-+
tert-Bu0.
+ C1.
+ H2C= C -CH2-+ I I c1 c1 1
(1)
tert-BuOH
1
H,C=C-C. l ,,slw.CH~-C
I
+
= CH
1
c1 c1
c1
H /
/H
CH2=IFc,*:;\1
/
CH,=C-CHCl?
+tert-rcl
C1CH2-C
I
c1
I
= CHCl
(3)
+ tert-BuO
c1
+ C H 2 = C -CH2C1 I c1 tert-BuOC1 + . C H = C -CH2C1 I c1 tert-BuOC1 + . C H = C-CH&l I c1 tert-Bu0.
mixed with the olefin. The flask was stoppered under nitrogen flow, and illuminated for several hours with direct sunlight or with a 100-watt electric light bulb. The latter was situated approximately 1 inch from the top of the flask, and enclosed in a shield of aluminum foil to contain approximately 90% of the incident radiation. During illumination, the temperature of the reaction mixture rose to approximately 35" from the absorbed radiation. Samples were withdrawn under nitrogen flow and analyzed by gas-phase chromatography, using a Varian-Aerograph Series 1200 gas chromatograph with flame-ionization detec-
+
.CH=C-CH2C1
I
+ tert-BuOH
(4)
c1 +
-
tert-BuO.
C1.
+ tert-Bu0 I
ClCHZ-C
I
.CH,-C
(5)
(6)
= CH
C1
++
+ ClCH=C-CHX1 I c1
1'
(7)
=C
C 'l
C1.
+ CH, = C-CH-OBu-tert I I c 1 c1
I
or tert-BuO-CH,-C
I n the above scheme, Reaction 2, which produces allylic radicals, will be greatly favored over Reaction 4, which does not. Experimental
2,3-Dichloropropene was collected from the Dow plant stream and purified b:y distillation. tert-Butyl hypochlorite was prepared by chlorinating tert-butyl alcohol (Teeter and Bell, 1952) (reagent grade) with chlorine from the Dow plant stream. Benzene was reagent grade, used without (further) purification. The individual cis and trans isomers of 1,2,3-trichloropropene were separated by fractional distillation of an approximately equimolar mixture obtained from the 1)ow Production Plant. They were then used to standardize the gas-liquid chromatograph. The sample containing 2,3-dichloropropene was pipetted into a 10-ml. nitrogen-swept flask, equipped with a standard-taper ground-glass stopper. Under nitrogen flow, tert-butyl hypochlorite was pipetted into and thoroughly
=C
I Cl
\
c'
1
tor, temperature programmer, and helium as carrier gas. The cis- and trans- isomers of the trichloropropene were identified by retention times in the gas chromatograph. Standard conditions were: oven temperature programmed from 100" to 150°C. a t 10" per minute; 130" injection temperature; 200" detector temperature; helium flow of 30 cc. per minute; hydrogen flow of 30 cc. per minute; air flow of 250 cc. per minute; and 1-p1. samples. "Dark" Reaction
A 15-ml. aliquant of 2,3-dichloropropene was mixed with 1 ml. of tert-butyl hypochlorite, and a portion of this mixture was transferred under nitrogen flow to a glass ampoule, which was then stoppered with a rubber serum cap. The ampoule was wrapped in aluminum foil to eliminate incident radiation, and the dark reaction was followed by periodically withdrawing samples from the ampoule, maintained a t approximately 25" C. The following data were obtained (initial mole ratio, tert-BuOCli 2,sdichloropropene = 0.052). VOL. 8 NO. 4 DECEMBER 1 9 6 9
461
Time, Hours
1,2,3-Trichloropmpene, Moles Mole tert-BuOC1
0.31 1.08 1.53 6 18 192
0.11 1.19 0.22 0.32 0.43 0.50
cis- and trans- isomers were formed in approximately equal amounts, and the sum of the two isomers is reported in Table I and plotted in Figure 1. The major by-product (other than tert-butyl alcohol) was identified as an ether by infrared spectroscopy. I t was presumed to be a tert-butoxy dichloropropene, but this identity has not been definitely established. Acknowledgment
The author gratefully acknowledges the assistance of Gerald J. Barrilleaux in determining the concentration of reactants and products by gas-phase chromatography.
Caserio, M. C., Pratt, R . E., Tetrahedron Letters 1, 91 (1967). Clarke, B. F., Jr., Chem. News 1931 265. Harford, C. G., U. S. Patent 2,179,787 (Nov. 14, 1939). Teeter, H. M., Bell, E. W., Org. Syntheses 32, 20 (1952). Walling, Cheves, “Free Radicals in Solution,” pp. 38690, Wiley, New York, 1957. Walling, Cheves, Heaton, La Donne, J . Am. Chem. SOC. 87, 38 (1965). Walling, Cheves, Heaton, La Donne, Tanner, D. D., J . 87, 1715 (1956). Am. Chem. SOC. Walling, Cheves, Jacknow, B. B., J . Am. Chem. SOC.82, 6108 (1960a). Walling, Cheves, Jacknow, B. B., J . Am. Chem. SOC.82, 6113 (1960b). Walling, Cheves, Kurkov, Viktor, J . Am. Chem. SOC.88, 4727 (1966). Walling, Cheves, Thaler, W., J . Am. Chem. SOC.83, 3877 (1961). Walling, Cheves, Wagner, P. J., J . Am. Chem. SOC.86, 3368 (1964). R . F. ROBERTS, J R .
Daw Chemical Co.
Literature Cited
Plaquemine, La.
Carlsson, D. J., Howard, J. A,, Ingold, K. U., J . Am. Chem. SOC.88, 4725-6 (1966).
70764 RECEIVEDfor review June 21, 1968 ACCEPTED August 8, 1969
LIQUID PERMEATION THROUGH ELECTRICALLY HEATED GELATIN MEMBRANES Membranes consisting of metallic screens impregnated with gelatin crosslinked with formaldehyde were developed for use in liquid permeation. The resulting membranes were insoluble in boiling water and electrically heated. Water was permeated through the membranes from upstream charges consisting of distilled water and various salt solution concentrations. Data were taken for various power inputs, membrane thicknesses, salt concentrations, and pressure differences across the membranes. With distilled water, the largest flow rate achieved was 4.14 Ib./hr. sq. ft. for a pressure difference of 4.04 p.s.i.; with a 5% salt solution, it was 3.26 Ib./hr. sq. ft. N o salt was present in the downstream fluid. To make effective use of the crosslinked gelatin membranes, it was necessary to have the heat source on the downstream side.
LIQUIDpermeation consists of separating the components of a liquid mixture by selective permeation of one of the components through a membrane (Binning et al., 1961). In this process the liquid charge mixture is maintained in contact with a thin barrier and the permeating product is removed from the opposite side of the membrane as a vapor. This process can be modified by using the concepts of suction boiling, which consists of boiling on a porous heat source-e.g., an electrically heated screenwith the generated vapor exhausting through the heat source itself (Wayner and Bankoff, 1965; Wayner and Kesten, 1965). Control is obtained in suction boiling by using a porous liquid feeder which utilizes the forces derived from interfacial free energy to supply liquid to the evaporating interface, control bubble nucleation, sep462
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
arate vapor from liquid, and direct the flow of vapor. I n the combined process, which is the topic of this communication, electrically heated metallic screens impregnated with crosslinked gelatin were used in the liquid permeation of water. This type of membrane process has potential industrial use-e.g., in the preparation of food extracts. Water readily dissolves into and diffuses through the gelatin membrane. If a heat source is located on the downstream side of the gelatin, it will retain its membrane characteristics. The electrically heated screen is both a good local source of heat and an ideal support for the membrane. I n large scale equipment, it may be desirable to modify the source of heat-e.g., by impregnated porous metal fins on a tube in which the recompressed vapor condenses. In a related patent applica-
