Organometallic compounds with acids

C. Reaction of Organometallic Compounds with Sulphurous Acid Derivatives... 

In some reactions of carbanions or organometallic compounds with very weak acids the base has a choice of protons and can give more than one salt. An example is the nuclear metallation of a substituted benzene in which the product may be oriented ortho, meta, or para. The actual results of a few such reactions are shown in Table XII. 

Carboxylic acid groups can also be installed in molecules using the reaction of an organometallic compound with carbon dioxide. This is a reductive method since the carbon dioxide is reduced to a carboxylic acid by formation of a new carbon-carbon bond. Both Grignard reagents and organolithium compounds work well in this reaction. 

The interaction of organometallic compounds with carboxylic acid chlorides and /V,/V-dimethylcarboxamides (Expt 5.94). 

THE INTERACTION OF ORGANOMETALLIC COMPOUNDS WITH CARBOXYLIC ACID CHLORIDES AND A DIMETHYLCARBOXAMIDES... 

With the usual reaction of organometallic reagents with acid derivatives (ester or acid chloride), the starting materials can add two equivalents of organometallic compound. The ketone generated after the first addition is quite reactive, and there is quite no selectivity between it and the starting acid derivative ... 

Acetylene is a Brpnsted acid (pA), 25). Its chemistry is associated with its triple-bond character and the labile hydrogen atoms. It can easily lose one proton to form the acetylide monoanion HC=C-(IUPAC name acetylenide) or release two to give the acetylide dianion C=C (C22-, IUPAC name acetylenedi-ide). The acetylenide H-C=C and substituted derivatives R-C=C- form organometallic compounds with the alkali metals. In these compounds, the interactions of the n orbitals of the C=C fragment with metal orbitals may lead to many structural types, e.g.,... 

Fig. 6.47. Top three reactions chemoselective acylations of weakly nucleophilic organometallic compounds with carboxylic acid chlorides.

Fig. 6.50. Acylation of organometallic compounds with various Weinreb amides (A, D and E) of carbonic acid.

We have already encountered one type of organometallic compound with a negative charge on carbon sodium acetylides, covered in Section 9-7. Terminal alkynes are weakly acidic, and they are converted to sodium acetylides by treatment with an unusually strong base, sodium amide. These sodium acetylides are useful nucleophiles, reacting with alkyl halides and carbonyl compounds to form new carbon-carbon bonds. 

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