Alkyl chlorides, dehydrochlorination

The direct reaction of other alkyl chlorides, such as butyl chloride, results in unacceptably low overall product yields along with the by-product butene resulting from dehydrochlorination. AH alkyl haHdes having a hydrogen atom in a P- position to the chlorine atom are subject to this complication. 

The possibility of an attack by the drying agent on the compound to be dried must always be considered carefully and if necessary examined by small-scale tests, as has been mentioned before. Most notable for such unwanted aggression amongst the popular drying agents is the molecular sieve. Various grades of molecular sieve have different activities and specialist publications should be consulted for details. The main reactions which must be kept in mind are that they can catalyse the dehydrochlorination of alkyl chlorides and the condensation of ketones, they can dehydrate alcohols and can form exposive compounds from nitroalkanes (see Section 4.6.3.). 

Tertiary alkyl chlorides are easily dehydrochlorinated by base (via the E2, or bimolecular elimination reaction mechanism), but the environment of the degrading resin is not basic. Loss of hydrogen chloride to yield an olefin can occur principally by the El, or monomolecular elimination reaction. This is a slow reaction because, in the rate-determining step, the C—Cl bond is broken to form two separated oppositely charged particles. The reaction rate is not assisted by the acid present. 

Several investigations77,88,90 indicated that steric factors do not determine the velocity of dehydrochlorination in branched alkyl chlorides, and the paramount factor which determines the rate of HC1 elimination is electronic in nature. 

Thermal dehydrochlorination of 1,1-dichloroethane at about 820 K is generally used for the production of vinylchloride. However, the process suffers from heavy coke deposition on the reactor walls, and catalytic reactions operating at lower temperatures were investigated in industry. Carbons were found to catalyze the dehydrochlorination (DHC) of alkyl chlorides to the corresponding alkenes. This reaction had been studied in 1933 for its suitability in the production of vinyl chloride. A list of early patents is given in ref. 170. Formation of 1-butene from... 

In the dehydrochlorination of alkyl chlorides, dimerization of the alkyl radicals was observed after splitting off of Cl ions (Section 7.5). This is also an indication that electrons from the carbon are involved. 

The chlorination of paraffins first produces a so-called chloro-oil , which contains around 30% alkyl chlorides and 70% paraffins. The chloro-oil is dehydro-chlorinated in a dehydrochlorination column, with a bottom temperature of around 300 °C. The resulting olefin/paraffin mixture is mixed with a larg molar excess of benzene and fed into the reactor, which is fitted with a powerful stirrer and cooling pipes. Here, the benzene is alkylated in the presence of hydrogen fluoride at a temperature below 50 °C. The reaction product is then separated into two layers in a separation vessel the upper layer, the crude alkylate, is split by distillation into benzene, an inter-cut, paraffin, alkylbenzene and a higher-boiling tail product. The hydrogen fluoride, which is present in the lower layer, is recirculated. 

Chlorination tower 2 Hydrogen chloride scrubber 3 Dehydrochlorination column 4 Alkyl chloride separation column 5 Degassing column 6 Alkylation reactor 7 Separator... 

Attempts to prepare 5-vinyl-5F7-dibenz[b,/]azepine by alkylation of 5i/-dibenz[b,/]azepine with 2-chloroethyl-p-toluenesulfonate followed by dehydrochlorination, or by direct vinylation with acetylene under pressure in toluene or in dimethyl sulfoxide, have failed.194 Also, 5H-dibenz[b,/]azepine fails to react with acryloyl chloride, although the 5-acryloyl derivative 8 (R = COCH = CH2 mp 122 — 123 C) has been prepared in 65% yield by condensing dibenz-azepine 5 with 3-chloroacryloyl chloride, followed by dehydrochlorination of the product with l,8-diazabicyclo[5.4.0]undec-7-ene in dimethyl sulfoxide at 80-90°C.194... 

Both methyl acrylate and butyl acrylate have been used to prepare vinylidene chloride copolymers with sufficient stability to permit thermal processing. The presence of alkyl acrylate units in the polymer mainchain limits the size of vinylidene chloride sequences and thus the propagation of degradative dehydrochlorination. More importantly it lowers the melt... 

Devulcanization in the Presence of Benzyl Chloride and Methyl Chloride. The above results suggest that catalyst efficiency might be improved when devulcanization is carried out with added alkylating agent. We find that this is, indeed, the case. Added benzyl chloride or methyl chloride further decreases the crosslink density for a given concentration of catalyst (Table 11). However, 1- and 2-chlorobutanes appear to be ineffective, possibly because of dehydrochlorination. 

Alkanesulfonyl chlorides are known to be a good source of alkanesulfonyl radicals or alkyl radicals with the aid of redox catalysts [3]. A series of studies using RuCl2(PPh3)3 as the redox catalyst have been carried out by Kamigata and coworkers (Scheme 13.6) [33-39]. Arenesulfonyl chlorides add to styrene derivatives to form the corresponding adducts, which undergo dehydrochlorination of EtsN to form the unsaturated sulfones [33]. When styrylsulfonyl chlorides are used as the precursor. 

In contrast, the corresponding alkyl carbamoyl chlorides are relatively stable, and require the presence of base and temperatures of ca. 100 C in order to undergo dehydrochlorination efficiently [1409]. 

When 7,7-dichlorobicyclo[4.1.0]heptane was reacted with potassium tert-butoxide in dimethyl sulfoxide in the presence of a C-H acid, elimination of hydrogen chloride, giving 7-chloro-bicyclo[4.1.0]hept-l(7)-ene, was followed by addition to the cyclopropene of the carbanion obtained from the C-H acid. The course of reaction was sensitive to several factors, among which the C-H acid employed was of significant importance. -Thus, when diethyl mal-onate was used several benzene derivatives were obtained and alkyl-substituted cyclopropanes were afforded, but in low yields. However, dehydrochlorination in the presence of 2-phenyl-propanonitrile gave 2-(bicyclo[4.1.0]hept-5-en-l-yl)-2-phenylpropanonitrile (1) and minor amounts of 2-ethyltoluene. ... 

No direct data for the decomposition of alkyl halides by clean, active metal surfaces seem to be available. Campbell and Kemball [11], in their study of the hydrogenolysis of ethyl chloride, cite evidence for the dehydrochlorination reaction... 

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