Dehydrogenation Dehydrohalogenation

Example dehydrogenation, dehydrohalogenation, dehydration Two possible mechanisms El and E2 Slow Step Fast Step... 

P Elimination Reaction in which a double or triple bond is formed by loss of atoms or groups from adjacent atoms. (See dehydration, dehydrogenation, dehydrohalogenation, and double dehydrohalogenation.)... 

Alkenylbenzenes are prepared by the various methods described m Chapter 5 for the preparation of alkenes dehydrogenation dehydration and dehydrohalogenation... 

Dehydrogenation of alkylbenzenes although useful m the industrial preparation of styrene is not a general procedure and is not well suited to the laboratory prepara tion of alkenylbenzenes In such cases an alkylbenzene is subjected to benzylic bromi nation (Section 11 12) and the resulting benzylic bromide is treated with base to effect dehydrohalogenation... 

There are few examples of the formation of benzazepines by dehydrogenation of their hydro derivatives. However, processes involving dehydrohalogenation and dehydration are more common. 

Cyclohepten-l-one has been prepared from cycloheptanone by dehydrohalogenation of the ethylene ketals of 2-chloro- and 2-bromocycloheptanone and subsequent hydrolysis. The a,)3-dehydrogenation of cycloheptanone has also been effected via the... 

Dehydrogenation of hydrazo compounds with bromine, 32, 16 Dehydrohalogenation by sodium amide, 30, 72... 

The procedure described is essentially that of Ballard and Dehn.1 Stilbene has also been prepared by reduction of desoxy-benzoin,20 benzaldehyde,23 and benzil 2o-2c by dehydrogenation of ethyl benzene,30 toluene,30- 33- 3, and bibenzyl 33-3alkaline reduction of phenylnitromethane,40 phenylnitroacetonitrile,40 and desoxybenzoin 43 by distillation of benzyl sulfone,50 benzyl sulfide,60-63 calcium cinnamate,5 cinnamic acid,5d phenyl cinna-mate,6e-6/ and diphenyl fumarate ie by dehydrohalogenation of a,a -dichlorobibenzyl60 and benzyl chloride 63 by dehalogenation of a,a,c/,a -tetrachlorobibenzyl70 and benzal chloride 73 by the coupling of cinnamic acid and phenyldiazonium chloride 8 by de-... 

Different procedures of this dehydrogenation are thoroughly discussed in the monograph (4). It is only necessary to note here that the process is carried out mainly as halogenation-dehydrohalogenation. The intermediate hydroximoyl halide is frequently not isolated (Scheme 1.3). The reaction is convenient for both the generation of unstable nitrile oxides (in the presence of a dipolarophile) and the preparation of stable nitrile oxides. It is usually carried out in a two-phase water-organic solvent system with methylene dichloride as the preferred solvent. 

The synthesis of fully unsaturated azepines by dehydrohalogenation or dehydrogenation of hydroazepines is an obvious ploy. However, such methods have met with mixed success,... 

Alkanes appear to react with platinum(IV) in an identical manner to benzene (34, 84) chloromethane and chloroethane can be detected as the reaction products from methane and ethane, respectively. When propane, butane, or hexane is the reactant, the terminal chloro isomers predominate over the internal isomers. This was interpreted to mean that primary C—H bonds are the most reactive (34), but a more detailed study has shown that this conclusion does not necessarily follow from the experimental results (84). When cyclohexane is the reactant, dehydrogenation (or chlorination and then dehydrohalogenation) occurs to give benzene as one of the reaction products (29, 34, 84). 

Azlactone oxidation Azlactones derived from dipeptides are more readily dehydrogenated than the dipeptides. This route to dehydropeptides has been examined with several reagents. Halogenation dehydrohalogenation is possible, but yields at best are 50%. Various oxidation procedures are about as effective. The most satisfactory method is oxidation of the corresponding trimethylsilyl enol ether with DDQ. However, this oxidation is limited to aryl azlactones. 

Dehydrocortisone, 87 8-Dehydroestradiol, 4 9(ll)-dehydroestradioI 3-methyl ether, 2 8(14)-DehydroestradioI 3-methyl ether, 3 Dehydrofluorination, 452 Dehydrofluorination of gem-difluorides, 446 Dehydrogenation, 306 Dehydrohalogenation of a-Halo ketones, 287 16-Dehydropregnenolone, 40 16-Dehydropregnenolone acetate, 48 16-Dehydropregnenolone tetrahydropyranyl ether, 40... 

Davy reagents 32,38 decarboxylation 64,67 Dehydrogenation of ketones 55 Dehydrohalogenation 57 Deracemization 68 Desulfurization 75 of dithioacetals 78,100 of dithioesters 69... 

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