Bromine, reaction with aldehydes

The reaction with bromine is very rapid and is easily carried out at room temperature, although the reaction is reversible under some conditions. In the case of bromine, an alkene-Br2 complex has been detected in at least one case. Bromine is often used as a test, qualitative or quantitative, for unsaturation. The vast majority of double bonds can be successfully brominated. Even when aldehyde, ketone, amine, so on functions are present in the molecule, they do not interfere, since the reaction with double bonds is faster. 

Mixed vapors of acrolein and ethyl alcohol were passed over the catalyst in a heated stainless steel tube at atmospheric pressure. Products were condensed and fractionated in a 20-plate bubble tray column. Fractions taken were acetaldehyde, 20-36°, and acrolein-ethyl alcohol, 36-78.4°. At this point water was added to the distillation kettle and an ethyl alcohol-aUyl alcohol-water fraction, 78-95°, was taken overhead. Fractions were analyzed for aldehydes by the hydroxylamine hydrochloride method, for im-saturation by reaction with bromine in aqueous potassium bromide, for alcohol by the nitrite ester method, and for water with Fischer reagent. Propyl alcohol in the water-free allyl alcohol recovered from the azeotrope was calculated by difference from the total alcohol determined by reaction with acetyl chloride and the unsaturated alcohol determined by reaction with aqueous bromine solution. Fresh catalyst was used for each experiment. 

Some ketones and aldehydes react with bromine to give a substitution product, but this reaction is slow except for ketones that have a high enol content. When substitution occurs, not only is the bromine color discharged, but hydrogen bromide gas is also evolved. 

The carboranyl Grignards do not appear to be as generally useful as the lithium derivatives in that they do not react with aldehydes or ketones 334). However, reported reactions with bromine, allyl bromide, or water proceed as might be expected 327, 334). 

Oxidation with bromine (Section 25.19) When a preparative method for an aldonic acid is required, bromine oxidation is used. The aldonic acid is formed as its lactone. More properly described as a reaction of the anomeric hydroxyl group than of a free aldehyde. 

A particularly common cr-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their a- positions by reaction with Cl2, Br2, or I2 in acidic solution. Bromine in acetic acid solvent is often used. 

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... 

Broadband-decoupled NMR, 451 Bromine, reaction with aldehydes, 846-848... 

Allylmagnesium bromide, 41, 49 reaction with acrolein, 41, 49 5-Allyl-l,2,3,4,5-pentachlorocyclopen-tadiene, 43, 92 Allyltriphenyltin, 41, 31 reaction with phenyllithium, 41, 30 Aluminum chloride, as catalyst, for isomerization, 42, 9 for nuclear bromination and chlorination of aromatic aldehydes and ketones, 40, 9 as Friedel-Crafts catalyst, 41, 1 Amidation, of aniline with maleic anhydride, 41, 93... 

Taurine is generally prepared from ox bile1 or the large muscle of the abalone.2 It has been synthesized from isethionic add through chloroethanesulfonic acid followed by the action of aqueous ammonia 3 from ethyleneimine and sulfur dioxide 4 from 2-mercaptothiazoline by oxidation with bromine water 5 from bromoethylamine and ammonium sulfite 6 and from acetaldehyde by a complex set of reactions involving sulfonation, formation of the aldehyde ammonia and the imido sulfonic add and finally reduction.7 The method given in the procedure has recently appeared in the literature.8 9... 

To investigate the feasibility of employing 3-oxidopyridinium betaines as stabilized 1,3-dipoles in an intramolecular dipolar cycloaddition to construct the hetisine alkaloid core (Scheme 1.8, 77 78), a series of model cycloaddition substrates were prepared. In the first (Scheme 1.9a), an ene-nitrile substrate (i.e., 83) was selected as an activated dipolarophile functionality. Nitrile 66 was subjected to reduction with DIBAL-H, affording aldehyde 79 in 79 % yield. This was followed by reductive amination of aldehyde x with furfurylamine (80) to afford the furan amine 81 in 80 % yield. The ene-nitrile was then readily accessed via palladium-catalyzed cyanation of the enol triflate with KCN, 18-crown-6, and Pd(PPh3)4 in refluxing benzene to provide ene-nitrile 82 in 75 % yield. Finally, bromine-mediated aza-Achmatowicz reaction [44] of 82 then delivered oxidopyridinium betaine 83 in 65 % yield. 

Benzotriazol-l-yl)methyl]triphenylphosphonium chloride 848 reacts with BunLi and aldehydes to give l-(alken-l-yl)benzotriazoles 849. Addition of bromine to the double bond of derivatives 849 followed by a reaction with amines furnishes amides 850. A variety of primary or secondary amines can be used. This way aldehydes are conveniently homologated and converted to amides with a one-atom longer chain (Scheme 136) <2004ARK(ix)44. 

Several trivial but highly useful reactions are known to convert one acceptor-substituted allene into another. For example, the transformation of allenic carboxylic acids is possible both via the corresponding 2,3-allenoyl chlorides or directly to 2,3-allen-amides [182,185], Allenylimines were prepared by condensation of allenyl aldehydes with primary amines [199]. However, the analogous reaction of allenyl ketones fails because in this case the nucleophilic addition to the central carbon atom of the allenic unit predominates (cf. Section 7.3.1). Allenyl sulfoxides can be oxidized by m-CPBA to give nearly quantitatively the corresponding allenyl sulfones [200]. The reaction of the ketone 144 with bromine yields first a 2 1 mixture of the addition product 145 and the allene 146, respectively (Scheme 7.24). By use of triethylamine, the unitary product 146 is obtained [59]. The allenylphosphane oxides and allene-... 

The kinetics of the reaction of bromine atoms with simple aliphatic aldehydes have been measured by the fast-flow technique with resonance fluorescence detection, and by laser flash photolysis. 

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