Sodium amide, reaction with alkynes

Double dehydrohalogenation (Section 9 7) Reaction in which a geminal dihahde or vicinal dihahde on being treated with a very strong base such as sodium amide is converted to an alkyne by loss of two protons and the two halogen substituents... 

The amide ions are powerful bases and may be used (i) to dehydrohalogenate halo-compounds to alkenes and alkynes, and (ii) to generate reactive anions from terminal acetylenes, and compounds having reactive a-hydrogens (e.g. carbonyl compounds, nitriles, 2-alkylpyridines, etc.) these anions may then be used in a variety of synthetic procedures, e.g. alkylations, reactions with carbonyl components, etc. A further use of the metal amides in liquid ammonia is the formation of other important bases such as sodium triphenylmethide (from sodamide and triphenylmethane). 

A terminal alkyne is an alkyne that has a hydrogen substituents (Fig. H). This hydrogen substituent is acidic and can be removed with strong base (e.g. sodium amide NaNH2) to produce an alkynide (Fig. I). This is an acid-base reaction. 

Carbon nucleophiles are very useful species because their reactions with carbon electrophiles result in the formation of carbon—carbon bonds. Section 10.8 introduced acetylide anions as nucleophiles that could be used in Sm2 reactions. These nucleophiles are prepared by reacting 1-alkynes with a strong base such as sodium amide. The relatively acidic hydrogen on the. vp-hybridized carbon is removed in this acid-base reaction ... 

The procedure for the final elimination reaction is essentially that of Rosenblum, et al.2 A more detailed procedure is provided which improves reproducibility. Treatment of an ethereal solution of (2-formyl-1-chlorovinyl)ferrocene with sodium amide in liquid ammonia under anhydrous conditions is also an acceptable method,5 along with the method described which employs base-induced elimination using aqueous sodium hydroxide in dioxane.2 6 Compounds of the n-haloferrocene type are converted more or less quantitatively into alkynes by dehydrochlorination using... 

Reaction with an amine, AIBN, CO and a tetraalkyltin catalyst also leads to an amide.Benzylic and allylic halides were converted to carboxylic acids electroca-talytically, with CO and a cobalt imine complex. Vinylic halides were similarly converted with CO and nickel cyanide, under phase-transfer conditions.Allylic (9-phosphates were converted to allylic amides with CO and ClTi=NTMS, in the presence of a palladium catalyst. Terminal alkynes were converted to the alkynyl ester using CO, PdBr2, CuBr2 in methanol and sodium bicarbonate. ... 

Elimination reactions can also be used to prepare alkynes. Dihalides can be converted into alkynes by treatment with base, provided that the two halogen atoms are on the same, or adjacent, carbon atoms. In general, alkyne formation requires more drastic reaction conditions than alkene formation, and a strong base, such as sodium amide, is usually employed (Reactions 5.4 and 5.5). The product of Reaction 5.5, phenylethyne, is shown in Figure 5.1 as a ball and stick model. 

This reaction was first reported by Bourguel in 1925. It is the synthesis of alkynes by the treatment of 2,3-dibromo-l-propene with a Grignard reagent to form a 3-substituted 2-bromo-l-propene, which further reacts with sodium amide. The yields are normally very high. Another advantage of using sodium amide in the last step is that other internal alkynes can isomerize to terminal alkynes. ... 

Most terminal alkynes (alkynes with a proton attached to a triply bonded carbon) have pA values of about 25 therefore, all react with sodium amide in liquid ammonia in the same way that ethyne does. The general reaction is... 

The yield of product from the carbon dioxide reaction with the alkyne anion was very poor, as it was with the vinyl Grignard derived from 1.166. Extending the carbon chain between the triple bond and the dimethylamino group, as in the reaction of 1.170 with sodium amide and then carbon dioxide, - however, led to... 

In the next chapter, we will learn a method for preparing alkynes (compounds containing C C triple bonds). In the following reaction, a dihalide (a compound with two halogen atoms) is treated with an excess of strong base (sodium amide), resulting in two successive E2 reactions. Draw the mechanism for this transformation. 

Alkynide ions react with carbonyl groups in much the same way as Grignard reagents do. We recall that these ions are effective nucleophiles that will displace a hahde ion ftom an alkyl halide to give an alkylated alkyne. The alkynides are prepared in an acid-base reaction with acetylene or a terminal alkyne using sodium amide in ammonia. If a carbonyl compound is then added to the reagent, an alcohol forms after acid work-up. If the alkynide is derived ftom acetylene, an acetylenic alcohol forms. 

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