Bromine, reaction with aldehydes compounds

The synthesized compounds were prepared by means of the Wittig reaction. The appropriate phosphoranes were obtained from commercially available aldehydes (through reduction, bromination, reaction with triphenylphosphine, and treatment with bases) and reacted with the required aldehydes. Mixtures of the E and Z stereoisomers in variable ratios were obtained and separated by chromatography. 

Chlorine and bromine react with aldehydes and ketones to give (X-halogenated compounds. The number of halogen atoms incorporated depends on reaction conditions. 

Excess of bromine converts each methylpteridine compound into the dibromomethyl derivative which on hydrolysis gives good yields of the corresponding aldehyde. An interesting variation of the reaction conditions was found in the treatment of the C- methylpteridines with POBra, which leads to the same mono- and di-bromomethyl derivatives. 6-Methylpterin reacts with more difficulty and with an excess of bromine in hydrobromic acid forms the... 

Carbonyl compounds are in a rapid equilibrium with called keto-enol tautomerism. Although enol tautomers to only a small extent at equilibrium and can t usually be they nevertheless contain a highly nucleophilic double electrophiles. For example, aldehydes and ketones are at the a position by reaction with Cl2, Br2, or I2 in Alpha bromination of carboxylic acids can be similarly... 

You should look upon silyl enol ethers as rather reactive alkenes that combine with things like protons or bromine (Chapter 21) but do not react with aldehydes and ketones without catalysis they are much less reactive than lithium enolates. As with alkylation (p. 674), a Lewis acid catalyst is needed to get the aldol reaction to work, and a Ti(IV) compound such as TiCl4 is the most popular. 

Chlorine and bromine react violently with these compounds, and with the aliphatic aldehyde compounds the following reaction takes place quantitatively in ether solution, and titration with standard iodine may be carried out ... 

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