2.3- Dibromosuccinic acid

Halogenation. Succinic acid and succinic anhydride react with halogens through the active methylene groups. Succinic acid heated in a closed vessel at 100°C with bromine yields 2,3-dibromosuccinic acid almost quantitatively. The yield is reduced in the presence of excess water as a result of the formation of brominated hydrocarbons. The anhydride gives the mono- or dibromo derivative, depending on the equivalents of bromine used. 

A solution of potassium hydroxide is prepared by dissolving 122 g. (2.2 moles 1.5 times the theoretical amount) of potassium hydroxide in 700 cc. of 95 per cent methyl alcohol (Note 1) contained in a 2-1. round-bottomed flask provided with a reflux condenser. To this alkaline solution is added 100 g. (0.36 mole) of a, /3-dibromosuccinic acid (p. 17), and the mixture is refluxed for one hour and fifteen minutes on a steam bath. The reaction mixture is cooled and filtered with suction. The mixed salts are washed with 200 cc. of methyl alcohol (Note 2), and dried by pressing between filter papers when dry the product weighs 144-150 g. 

These terms are best illustrated by examples. Thus, if maleic acid treated with bromine gives the dl pair of 2,3-dibromosuccinic acid while fumaric acid gives the meso isomer (this is the case), the reaction is stereospecific as well as stereoselective because two opposite isomers give two opposite isomers ... 

There is much evidence that when the attack is by Br (or a carrier of it), the bromonium ion (2) is often an intermediate and the addition is anti. As long ago as 1911, McKenzie and Fischer independently showed that treatment of maleic acid with bromine gave the dl pair of 2,3-dibromosuccinic acid, while fumaric acid (the... 

CjHjBrjN 626-05-1) see Acrivastine meso-2,3-dibromosuccinic acid (C4H4Br204 608-36-6) see Biotin... 

Maleic acid when treated with bromine gives dl pair of 2, 3 dibromosuccinic acid while fumaric acid gives the meso isomer. 

Similarly the addition of bromine to maleic acid giving a racemic mixture of dibromosuccinic acid is again a trans addition. Here also there is first the formation of a bridged (or a non-classical) carbocation followed by the attack of the bromide ion. The various steps are as follows ... 

Any reaction in which only one of a set of stereoisomers is formed exclusively or predominantly is called a stereoselective synthesis.184 The same term is used when a mixture of two or more stereoisomers is exclusively or predominantly formed at the expense of other stereoisomers. In a stereospecific reaction, a given isomer leads to one product while another stereoisomer leads to the opposite product. All stereospecific reactions are necessarily stereoselective, but the converse is not true. These terms are best illustrated by examples. Thus, if maleic acid treated with bromine gives the dl pair of 2,3-dibromosuccinic acid while fumaric acid gives the meso isomer (this is the case), the reaction is stereospecific as well as stereoselective because two opposite isomers give two opposite isomers ... 

Preparation 349.—Dibromosuccinic Acid [2 3-Dibromo-butan-diacid],... 

Apart from a change in the course of the reduction, which will be discussed below in the section on stereospecific electrosynthesis, the epimers of a,a -dibromosuccinic acid show differences in half-wave potentials (134,135). The free acid of the erythro dibromosuccinic acid is reduced at more positive potentials than the threo-ioxm. For the anions of these acids, however, the reduction at higher pH values occurs at more positive potentials for the threo-epimer than for the erythro-anion. For the esters of dibromosuccinic acids, the difference in half-wave potentials of the two epimers is too small to be significant. 

Electrosynthesis is useful when the electrode reaction is stereo specific. For example, for a,a -dibromosuccinic acids, the threo form of both the free acid and its anions is reduced to fumaric acid. On the contrary, the erythro epimer is reduced to fumaric acid only in the undissociated form and as a dibasic anion. The univalent anion is at least partly reduced to maleic acid. Both threo and erythro epimers of dialkyl esters of dibro-mosuccinic acid are reduced, similarly to the undissociated free acids, to only the dialkyl ester of fumaric acid (134,135). 

This term was introduced to the normal chemical language in the 20th century due to the efforts of Bodenstein. In Semenov s view, the understanding that, no matter how complicated is a reaction s process the law of the elementary act is sufficiently simple, is exclusively the credit "of Van t Hoff s genius prediction, though he himself did not understand it quite clearly [5, p. 6]. Though the epithet "genius with respect to Jacob Henri Van t Hoff is still valid, the situation, however, defies its complete reconstruction. On the one hand, it is likely that Van t Hoff renounced in principle the analysis of complex reactions that do not obey the laws of "normal conversions . Apparently, it is for this reason that in the "Etudes he did not examine etherification reactions practically [19]. Van t Hoff studied such simple reactions as the decomposition of dibromosuccinic acid and the reaction of... 

The most frequently occurring rotation/reflection axis in organic chemistry is, S the intramolecular mirror plane. Its presence makes ci.v-1,2-dibromocyclohexane (structure A in Figure 33) as well as ma o-2,3-dibromosuccinic acid (structure B) achiral. This is true even though there are two stereocenters in each of these compounds. But why is the dibromocy-clohexane dicarboxylic acid C (Figure 3.3) achiral The answer is that it contains an S2 axis, an inversion center, which occurs rarely in organic chemistry. This compound is thus achiral although it contains four stereocenters. 

This is supported by the fact that the reaction with fumaric acid gives meso-dibromosuccinic acid, whereas maleic acid gives the chiral dibromosuccinic acid, of course as a racemic mixture. Note that these reactions are stereospecific. 

Note that according to the foregoing definition, chirality occurs only in molecules that do not have a rotation/reflection axis. However, if the molecule has only ( ) an axis of rotation, it is chiral. For example, both trans-1,2-dibromocyclohexane (D in Figure 3.3) and the dibromosuccinic acid E have a two-fold axis of rotation (C2) as the only symmetry element. In spite of that, these compounds are chiral because the presence of an axis of rotation, in contrast to the presence of a rotation/reflection axis, is not a criterion for achirality. 

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