660. The chlorination of some n-alkanes and alkyl chlorides

Abstract

The liquid-phase chlorination of n-hexane, n-octane, 1-, 2-, and 3-chlorohexane, and l-chloro-octane, using elemental chlorine, has been studied a t 20". Product yields of the mono and higher chlorides, together with unreacted n-hexane, have been compared with a statistical rrAodel for the chlorination of alkanes. The overall reactivities of the individual reactants have been measured, relative to n-hexane, and are in the order: n-octane > n-hexane = l-chloro-octane > l-chlorohexane > 2-chlorohexane > 3-chlorohexane. Yields of the monochlorides from the n-alkanes and dichlorides from the monochloroalkanes, respectively, have been determined by means of gas-chromatographic analysis. Relative selectivities for the abstraction of hydrogen by atomic chlorine have been calculated. In addition, the yields of the diastereoisomeric forms of 2,3-, 2,4-, and 2,5-dichlorohexane derived from 2-chlorohexane have been measured, and the steric course of the chlorination reaction is discussed.T H E chlorination of aliphatic hydrocarbons and their derivatives has been the subject of several reviews1 Of the chloro-alkanes investigated, those containing less than five carbon atoms have been studied in greatest detail. The chlorination of some higher alkyl chlorides has been reported by Horner and Schlafer.2 We have extended these studies by investigating the liquid-phase chlorination, at 20°, of the chloro-alkanes 1-, 2-, and 3-chlorohexane and l-chloro-octane, and, in addition, the two alkanes n-hexane and n-octane. The purpose of our work was to compare the product yields for an n-alkane with those predicted from a statistical model, and to study the reactivities of the chloroalkanes, directive effects, and the steric course of the chlorination reaction. EXPERIMENTAL I.C.I. cylinder chlorine, containing, in the initial fraction, 5-10y0 (v/v) oxygen, was deoxygenated before use by " bleeding off " the initial 10% (by weight) of the cylinder contents.The two hydrocarbons were shown by gas-chromatographic analysis to contain less than 1% (w/w) of aromatic and aliphatic hydrocarbons as impurities, and were used without further purification.Eastman-grade l-chlorohexane and l-chloro-octane were obtained from Kodak Ltd.3-Chlorohexane was prepared by reaction of hexan-3-01 with thionyl chloride. These materials contained trace impurities in the form of isomers and homologues of the corresponding chloro-alkanes. Chlorination did not result in the formation of any anomalous products.Apparatus and Procedure.-The alkane was weighed into the reaction vessel, consisting of a Materials.-Chlorine.This procedure reduced the oxygen concentration to 15-50 p.p.m. AZkanes. n-Hexane and n-octane were supplied by L. Light & Co.

Chlorinated Paraffins

“…Activated sludge from a sewage treatment plant, acclimated to n-hexadecane for 60 days, dechlorinated only 2% of a medium chain PCA (C 15.4 Cl 5.6 ). Fisk et al [36] found that four 14 C-labeled PCAs (two C 12 (56% and 69% Cl) and two C 16 (35% and 69% Cl) PCAs) were degraded at 12°C in aerobic sediments used for a study of bioavailability of PCAs in oligochaetes. Half lives of the C 12 -PCAs in sediment were 13 days and 30 days for the 56% and 69% Cl products, respectively, while for the C 16 -PCA, half lives of 12 days and 58 days for 35% and 69% Cl PCAs were observed.…”

“…However, in general, HLC values for PCAs do not show the large [22]. Reverse phase HPLC analysis of C 16 PCAs also yields log K OW values close to the range predicted by fragment constants [36]. Octanol-air partition coefficients of PCAs have not been measured directly but they can be estimated from the ratio of K OW /K AW (where K AW = unitless airwater partition coefficient).…”

“…Short-and medium chain commercial PCAs products with 50% Cl or more do not contain appreciate amounts (i.e., >0.1%) of mono-to tetrachloro-alkanes (Tomy G, unpublished data). Assuming one chlorine per carbon, since a second chlorine atom does not readily substitute for hydrogen at a carbon already bound to chlorine [16][17][18], and taking into account that isomers with four chlorines or less are not present, the theoretical number of positional isomers possible for C 10 -C 17 PCAs ranges from 327 for penta to decachloro-n-decane to 53,000 for penta-to heptadecachloro-heptadecane [9]. GC-MS analysis of commercial short chain PCA mixtures shows that hexa-and heptachloro-decanes, undecanes, and dodecanes are the predominant isomers [14].…”

Conformation preference and related intramolecular noncovalent interaction of selected short chain chlorinated paraffins

“…The dispersed chlorination mode of alkanes decides that the dihedral angle (H-C-C-Cl) receives the preference over (Cl-C-C-Cl) in hexa-and heptachloro-decanes, the predominant isomers in commercial SCCPs [9,33]. Therefore, the potential energy profiles for intramolecular rotation of the dihedral angles (H-C-C-Cl) were calculated at the B3LYP/6-311++G(d,p) level to shed more light on the influence of different intramolecular NCIs on the conformations of the two molecules.…”

“…Considering the dihedral angle (H-C-C-Cl) receives the preference over (Cl-C-C-Cl) in SCCPs due to its dispersed chlorination modes [9,33], the potential energy profiles for intramolecular rotation of the dihedral angles (H-C-C-Cl) for 5,5,6,6-tetrachlorodecane and 4,4,6,6-tetrachlorodecane have been calculated with (H-C-C-Cl) initially assigned the value 0°, respectively, to shed more light on the conformation preference of the two molecules ( Figure 1). The H-C-C-Cl dihedral angles are switched every 10° to obtain one starting geometry.…”