Elimination to form £-alkenes

When applied to the synthesis of ethers the reaction is effective only with primary alcohols Elimination to form alkenes predominates with secondary and tertiary alcohols Diethyl ether is prepared on an industrial scale by heating ethanol with sulfuric acid at 140°C At higher temperatures elimination predominates and ethylene is the major product A mechanism for the formation of diethyl ether is outlined m Figure 15 3 The individual steps of this mechanism are analogous to those seen earlier Nucleophilic attack on a protonated alcohol was encountered m the reaction of primary alcohols with hydrogen halides (Section 4 12) and the nucleophilic properties of alcohols were dis cussed m the context of solvolysis reactions (Section 8 7) Both the first and the last steps are proton transfer reactions between oxygens... 

When applied to the synthesis of ethers, the reaction is effective only with primary alcohols. Elimination to form alkenes predominates with secondary and tertiary alcohols. 

Carbanions derived from phosphine oxides also add to carbonyl compounds. The adducts are stable but undergo elimination to form alkene on heating with a base such as sodium hydride. This reaction is known as the Horner-Wittig reaction.268... 

Alcohols can react in several ways, depending on the reactants and on the conditions of the reaction. For example, alcohols can undergo substitution with halogen acids, elimination to form alkenes, and oxidation to form aldehydes, ketones, or carboxylic acids. 

Atkenes from sic-dihaiides. The reaction of /c-dihalides with NaSeCH3 or NaSeC6H5 in ethanol or THF-HMPT (3 1) results in alkenes. The reaction involves a formal a rr-elimination in the case of wc-dibromides or uie-chloroiodidcs, but a formal xyn-elimination in the case of w c-dichlorides. Elimination to form alkenes also occurs with /K-haloalkyl phenyl selenides. 

The involvement of carbocations accounts for the side reactions that accompany isomerization. Carbocations are known to undergo p scission to yield low-molecular-weight cracking products. They can also undergo proton elimination to form alkenes that, in turn, participate in condensation (oligomerization), cycli-zation, and disproportionation reactions. 

A. Krebs, J. Swienty-Busch, Eliminations to Form Alkenes, Allenes and Alkynes and Related Reactions, in Comprehensive Organic Synthesis (B. M. Trost, I. Fleming, Eds.), Vol. 6, 949, Pergamon Press, Oxford, 1991. 

Predict and explain the stereochemistry of E2 eliminations to form alkenes. Predict the products of E2 reactions on cyclohexane systems. 

Higher yields are obtained with chlorides, especially if no elimination to form alkenes... 

Oxetanes are synthesized from /(-halo alcohols under basic conditions. Chlorides,426-429 iodides,430 mesylates,431,432 or tosylatcs433 are used. Though different bases give good results, 1,8-diazabicyclo[5.4.0]undcc-7-ene seems to work best for the cyclization of alcohol 1 to oxetane 2.430 Higher yields are obtained with chlorides, especially if no elimination to form alkenes can occur.426,427... 

Alkyllithium reagents attack the unsubstituted carbon of terminal epoxides. In the presence of excess amide base, the intermediate alkoxides eliminate to form alkenes (Scheme 10) <2004JA12250>. 

There are other applications of these derivatives. For example, imines can be reduced to amines (equation 1), oximes can undergo rearrangement under strongly acidic (or dehydrating) conditions to form amides (equation 2), and the treatment of tosylhydrazones with strong bases can provide an excellent method for reductive elimination to form alkenes (equation 3). ... 

Eliminations to Form Alkenes, Allenes and Alkynes and Related Reactions... 

Rearrangement is sometimes observed on the addition of sulfur ylides to ketones, yielding a homologated ketone rather than the expected epoxide (equation 30). Hydroxy sulfides can undergo elimination to form alkenes, but the conditions are quite specific and require derivatization at oxygen or sulfur. ... 

Aluminum halide catalysts are not effective isomerization catalysts for hydrogenated chlorofluorocarbons because of HCl elimination to form alkenes which are catalyst poisons. HF elimination from hydrofluorocarbons is not as facile, thus AIF3 [63] and AIClxF, 02 (x + y + 2z = 3) [64] are effective catalysts for the isomerization of 134 to 134a (eq 13). 

In this mechanism the one-electron oxidation followed by trapping of the cation radicals on the surface leads to sulfite surface esters which can either ionize generating carbocations, or eliminate to form alkenes, both species being able to carry out carbocadon reactions. A mechanism of this type would be in agreement with the n-butanc isomerization mechanistic studies, which show that the reaction occurs via Cg intermediates. 

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