Cinnamic acid, bromine addition

But catalytic reduction of the same phenyl propionic acid gives cis cinnamic acid. Therefore by adding hydrogen under various conditions, one can obtain a desired isomer. The conversion of acetylene into olefinic compounds has been carried out not only for the sake of obtaining the adduct, but Michael studied the various addition reactions for the sake of obtaining a desired product cis or trans. For example, he found that the addition of bromine to acetylene-dicarboxylic acid leads predominantly to the formation of trans isomer. 

If these chemical chains involving Br or Br3 were ruled out, one could consider an energy chain, in which the exothermic heat of reaction plus the energy of excitation is sufficient to produce the dibromide of cinnamic acid with a high energy content. The heat of bromination alone is estimated at 16,000 calories. These hot molecules of product then pass their energy over to more bromine atoms which then react to form additional dibromide, as follows,... 

Examples of the solvent-dependent competition between nucleophilic substitution and / -elimination reactions [i.e. SnI versus Ei and Sn2 versus E2) have already been given in Section 5.3.1 [cf. Table 5-7). A nice example of a dichotomic y9-elimination reaction, which can proceed via an Ei or E2 mechanism depending on the solvent used, is shown in Eq. (5-140a) cf. also Eqs. (5-20) and (5-21) in Section 5.3.1. The thermolysis of the potassium salt of racemic 2,3-dibromo-l-phenylpropanoic acid (A), prepared by bromine addition to ( )-cinnamic acid, yields, in polar solvents [e.g. water), apart from carbon dioxide and potassium bromide, the ( )-isomer of l-bromo-2-phenylethene, while in solvents with low or intermediate polarity e.g. butanone) it yields the (Z)-isomer [851]. 

Phenylpropynoic acid (13) can be prepared from cinnamic acid esters by the addition of bromine to the double bond followed by dehy-drobromination with alcoholic potassium hydroxide (Scheme 5.14). 

Many solid-state reactions of all types rely on cleavage planes [1]. For example a-cinnamic acid 1 (Fig. 2.1.3) or anthracene 14 (Fig.2.1.13) with slightly inclined planar molecules in double or single layers are reactive in both solid-state photolysis and bromination [16]. The molecular packing of 35 is even more favorable for solid-state reactivity at its varied functionality (Fig. 2.1.21) as the molecules lie flat and as there is additional free space between the aromatic rings. The molecules 35 adopt the zwitterionic form with hydrogen bonds exclusively within the double layers. 

Addition of bromine to C=C bonds does not begin with electrophilic addition of Br+ nucleophilic mechanisms are possible. Thus, for instance, addition of bromine in glacial acetic acid to maleic or fumaric acid, stilbene, cinnamic acid, or tetrachloroethylene, which is normally slow, is catalysed by LiBr or KBr.20... 

Cinnamic acid, like other unsaturated compounds, forms addition-products with the halogen hydrides, hypochlorous acid, bromine, and so forth. It yields esters, an acid chloride, and an amide. The hydrogen atoms in the benzene ring may be replaced by the halogens, nitro groups, amino groups, and the sulphonic acid group. 

The high instability of bromine monochloride (the heat of formation of which has been estimated as 0.3 kcal.mole ) provides some difficulty in studying its reactions. Nonetheless, the rate of addition of mixtures of chlorine and bromine (with the total concentration of halogen constant) to c/s-cinnamic acid in carbon tetrachloride-acetic acid mixtures was greatest when [Br2]/[Cl-i] was unity . The kinetic form of the reaction was the same as that for the other interhalogens and for bromine, but not for chlorine. The possible intervention of bromine monochloride in the reaction of allyl trimethylammonium perchlorate with hypobromous acid in aqueous acid has also been reported here, the kinetics were . 

Reaction of frans-cinnamic acid with Br2 in solution gives erythro-2,3-dihrom.o-3-phenylpropionic acid. Addition of bromine to frans-cinnamic acid that has been coordinated with a dicobalt species in an organic capsule" gives )-threo-2,3-dibromo-3-phenylpropionic acid, however. What do these results suggest about the differing mechanisms of the two addition reactions ... 

As one of the enzymic reactions, asymmetric synthesis catalyzed by cyclodextrins has been studied in the past, but gave all the products in a low optical yield. We have already found a strong chiral induction for the chlorination of methacrylic acid in the crystalline cyclodextrin complexes. 100 % enantiomeric excess (e.e.) of (-)-2,3-dichloro-2-methyl-propionic acid and 88 % e.e. of its enantiomer were isolated in a- and 3-cyclodextrins, respectively. This paper describes asymmetric addition of gaseous halogens and hydrogen halides in the crystalline complexes comprising trans-cinnamic acid as a reactant and a- or 3-cyclodextrin as chiral matrix. Asymmetric bromination of menthyl cinnamate and of salts from the acid and several chiral amines have been reported, but gave low chiral inductions up to 2 16 % e.e.. 

In fact, at the end of the reaction of trans-cinnamic acid with chlorine under air, the sticky solid product was obtained, but with bromine no change of the solid was observed. However, when the addition of these reagents to the acid proceeded in the microcrystalline cyclodextrin matrix, there was no visual evidence of liquid phase on the crystal even in chlorination of it under microscope. 

Figure 2. Optical yields on asymmetric addition of bromine to trans-cinnamic acid in B-cyclodextrin cavity at various temperatures.

Table III shows the results of hydro-bromination and hydrochlorination of the ethyl trans-cinnamate inclusion complexes. No hydrochlorination was observed at various temperatures after long exposure of hydrogen chloride gas similar to the reaction of trans-cinnamic acid [14]. Addition of hydrogen bromide to the ester gave an optically active and regioselective product, ethyl R-(+)-3-bromo-3-phenyl-propanoate in 46 % e.e. from the a-cyclodextrin, or ethyl S-(-)-3-bromo-3-phenylpropanoate in 31 % e.e. from the 3-cyclodextrin inclusion complex.

The second stage (Experiment [D2]) involves the addition of bromine to the intermediate formed in the first step, frans-cinnamic acid. The product of this halogenation is e T/fizro-2,3-dibromo-3-phenylpropanoic acid. The stereochemistry involved in the formation of this second intermediate is a result of the nature of the anti addition of molecular bromine to a trans alkene. The details are given in the discussion in Experiment [D2]. 

Purpose. The bromination of frans-cinnamic acid is carried out to obtain en/flzro-2,3-dibromo-3-phenylpropanoic acid, the direct precursor to 2 -bromo-styrene, which is the synthetic target of Sequence D. You wiU review the stereospecificity of the addition of molecular bromine to an alkene. 

The result of the halogenation of frans-cinnamic acid, as in the case of (E)-stilbene in Experiment [A2b], is an anti addition of molecular bromine. The enantiomeric products are shown here ... 

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