Alkyl halides alcohol reactions with hydrogen

The major portion of the present chapter concerns the conversion of alcohols to alkyl halides by reaction with hydrogen halides... 

Two kinds of starting materials have been examined in nucleophilic substitution reactions to this point. In Chapter 4 we saw that alcohols can be converted to alkyl halides by reaction with hydrogen halides and pointed out that this process is a nucleophilic substitution taking place on the protonated fonm of the alcohol, with water serving as the... 

Alcohols and phenols are also weak bases. They can be protonated on the oxygen by strong acids. This reaction is the first step in the acid-catalyzed dehydration of alcohols to alkenes and in the conversion of alcohols to alkyl halides by reaction with hydrogen halides. Alkyl halides can also be prepared from alcohols to alkyl halides by reaction with hydrogen halides. Alkyl halides can also be prepared from alcohols by reaction with thionyl chloride or phosphorus halides. 

I. Reaction with hydrogen halides Alcohols react with hydrogen halides to form alkyl halides (Refer Unit 10, Class Xll). 

Write the steps in the mechanism for conversion of an alcohol to an alkyl halide upon reaction with a hydrogen halide. 

Section 4.11 The conversion of an alcohol to an alkyl halide on reaction with a hydrogen halide is a nucleophilic substitution. Nucleophilic substitutions (Sn) are classihed as S l or 8 2 according to whether the rate-determining step is unimolecular or bimolecular. 

Unlike tertiary and secondary carbocations, primary carbocations are too high in energy to be intermediates in chemical reactions. Since primary alcohols are converted, albeit rather slowly, to alkyl halides on treatment with hydrogen halides, they must follow some other mechanism that avoids carbocation intermediates. This alternative mechanism is believed to be one in which the carbon-halogen bond begins to form before the carbon-oxygen bond of the alkyloxonium ion is completely broken. 

Reactions of alcohols with hydrogen halides (Section 4.7) Alcohols react with hydrogen halides to yield alkyl halides. The reaction is useful as a synthesis of alkyl halides. The reactivity of hydrogen halides decreases in the order HI > HBr > HCI > HF. Alcohol reactivity decreases in the order tertiary > secondary > primary > methyl. 

Alcohols react with hydrogen halides (HX) to give alkyl halides. Primary alcohols undergo Sn2 reactions with HX. Primary alcohols with branching on the P-carbon give rearranged products. The temperature must be kept low to avoid the formation of E2 product. 

When alkyl halides are treated with KOH in an alcohol solution at high temperatures, alkenes are produced. Such reactions in which a hydrogen halide is removed from the compound are called dehydrohalogenation reactions. 

The reaction of alcohols, alkyl halides or alkenes with alkenes in the presence of anhydrous hydrogen fluoride should lead to conjugated alkylation of the alkenes with simultaneous introduction of an alkyl group and a fluorine atom to give products 1. 

Alcohols react with hydrogen halides to produce alkyl halides. In these reactions, the —OH group of the alcohol is replaced by the halide ion of the acid. All alcohols react with concentrated HBr and HI solutions to produce alkyl bromide and alkyl iodide. These reactions occur by a specific mechanism as shown below. 

The value of thiourea for the preparation of thiols is that on reaction with alkyl halides,271 mixtures of hydrogen bromide and alcohols,272 or suitable aromatic273 or heterocyclic halides274 it readily yields S-alkyl- or S-aryl-thiouronium salts, from which the thiols are usually obtained in good yield by alkaline hydrolysis or by aminolysis with high-boiling, strongly nucleophilic... 

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