Alkyl halides hydrocarbon formation

This reaction can be used for the synthesis of hydrocarbons but it may also take place as a side-reaction during generation of a Grignard reagent from an alkyl halide and magnesium, then leading to formation of undesired side-products. 

Chemiluminescence also occurs during electrolysis of mixtures of DPACI2 99 and rubrene or perylene In the case of rubrene the chemiluminescence matches the fluorescence of the latter at the reduction potential of rubrene radical anion formation ( — 1.4 V) at —1.9 V, the reduction potential of DPA radical anion, a mixed emission is observed consisting of rubrene and DPA fluorescence. Similar results were obtained with the dibromide 100 and DPA and/or rubrene. An energy-transfer mechanism from excited DPA to rubrene could not be detected under the reaction conditions (see also 154>). There seems to be no explanation yet as to why, in mixtures of halides like DPACI2 and aromatic hydrocarbons, electrogenerated chemiluminescence always stems from that hydrocarbon which is most easily reduced. A great number of aryl and alkyl halides is reported to exhibit this type of rather efficient chemiluminescence 155>. 

Organometallic compounds or carbanions undergo a number of reactions in which the carbanion or carbanion-like moiety of the organometallic compound acts as a nucleophilic displacing agent. Examples are the formation of hydrocarbons from alkyl halides, alkyl halides from halogens, and ketones from acid chlorides or esters. The latter two reactions are closely related to the base-catalyzed condensations and are perhaps additions as well as displacement reactions. Related addition reactions are the carbonation of organometallic compounds and the addition to ketones or aldehydes. 

Alkylation is a very broad reaction type and it can, depending on the nature of the alkylating agent, proceed either as a substitution or as an addition reaction. The alkylation by substitution of, for example, aromatic hydrocarbons, phenols or amines is based on the reaction with alkyl halides or alcohols. Some evidence indicates that, at least partly, the alkylation proceeds through the intermediate formation of alkenes from the alkylating agent when the reaction is conducted at atmospheric pressure and at high temperature. 

The results obtained in the gas-phase isopropylation of various aromatic hydrocarbons with isopropyl chloride over Nafion-H catalyst showed only a relatively small variation of reactivity in going from fluorobenzene to xylenes.235 Therefore, it has been assumed that the reaction rate is controlled by the formation of a reactive electrophilic intermediate (possibly, protonated alkyl halide 61, or some form of incipient alkyl cation) rather than by cr-complex formation between the electrophile and the aromatic nucleus [Eq. (5.89)]. 

The condensation of saturated hydrocarbons with haloolefins in the presence of anhydrous aluminum chloride also results in the formation of alkyl halides, as in the preparation of l-chloro-3,4-dimethylpentane from isobutane and allyl chloride (40%). Under the same conditions, alkyl halides react with olefinic halides to give dihaloalkanes. unsym-Heptachloropropane is synthesized from tetrachloroethylene and chloroform (93%). ... 

Preparation of Alkyl Halides.—We have spoken of the formation of the alkyl halides by the direct action of the halogen upon the saturated hydrocarbon. In the case of chlorine this action takes place at ordinary temperatures as in the reaction between methane and chlorine in the sunlight. Bromine, however, does not act directly at ordinary temperatures but by heating in a sealed tube. Iodine does not act directly with the hydrocarbons. In any case the result is a mixture of several substitution products, and the method is not, therefore, of practical value. Where direct action does not occur the presence of iodine chloride or antimony chloride, which act as carriers, is necessary. The two reactions of most importance in the preparation of these compounds are those involving either alcohols or unsaturated hydrocarbons. These will be taken up when these compounds are studied. 

The ethereal solutions of these iodides do not fume in air, and removal of the solvent gives a liquid, which on further heating evolves dense white fumes, probably of beryllium oxide. Heating changes the alkyl beryllium halides to beryllium dialkyls. All the alkyl halide compounds are decomposed by water, with formation of the corresponding hydrocarbon. When carbon dioxide is passed through ethereal beryllium methyl iodide for three hours, the solution still gives a positive test and no acetic acid is found after hydrolysis. Acetanilide is formed from beryllium methyl iodide and phenyl isocyanate. 

Alcohols react with HX to form alkyl halides, but the reaction works well only for tertiary alcohols, R,COH. Primaiy and secondary alkyl halides are normally prepared from alcohols using either SOClj or PBr ). Alkyl halides react with magnesium in ether solution to form organomagnesium halides, or Grignard ret ents (RM O- Since Grignard reagents are both nucleophilic and basic, they react with acids to yield hydrocarbons. The overall result of Grignard formation and protonation is the conversion of an alkyl halide into an alkane (RX— RM RH). 

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