Ethyl cinnamate hydrogenation

Phenylpropiolic acid. This is an example of an aromatic acetylenic acid, and is made by adding bromine to the ethylenio linkage in ethyl cinnamate, and treating the resulting dibromide with alcohobc potassium hydroxide which eliminates two molecules of hydrogen bromide ... 

The catalyst is inactive for the hydrogenation of the (isolated) benzene nucleus and so may bo used for the hydrogenation of aromatic compounds containing aldehyde, keto, carbalkoxy or amide groups to the corresponding alcohols, amines, etc., e.g., ethyl benzoate to benzyl alcohol methyl p-toluate to p-methylbenzyl alcohol ethyl cinnamate to 3 phenyl 1-propanol. 

With cobalt catalysts, hydroformylation of ethyl cinnamate gave 91% of the hydrogenation product ethyl hydrocinnamate (15) and only 8% of the expected lactone, 16 (72). However, rhodium catalysis was effective in directing the reaction in favor of hydroformylation (70). The comparative results obtained with cobalt and rhodium are outlined in Table XXV. 

The (Z)-ethyl cinnamate was obtained by hydrogenation of ethyl phenyl propiolate using Lindlar s catalyst (5% palladium on calcium carbonate, poisoned with lead) in w-hexane under an atmospheric pressure of hydrogen. The mixture, containing 75% of the (Z)-ethyl cinnamate, 22% of the overreduced alkane and 3 % of the (E )-ethyl cinnamate, was used without further purification. 666 mg of this mixture contains 500 mg of (Z)-ethyl cinnamate (2.55 mmol). 

Methyl cinnamate was reduced quantitatively to methyl 3-phenylpropa-noate by hydrogen over colloidal palladium at room temperature and atmospheric pressure [7057] ethyl cinnamate was reduced to ethyl 3-phenyIpropa-noate over tris(triphenylphosphine)rhodium chloride in ethanol at 40-60° and 4-7 atm in 93% yield [55], and over copper chromite at 150° and 175 atm in 97% yield [420]. On the other hand, hydrogenation of ethyl cinnamate over... 

Comparison of bromofluorinations of six substituted ethyl cinnamates using A-bromosuccin-imide with hydrogen fluoride/pyridine and hydrogen fluoride/tetrahydrofuran (several molar ratios) also shows a Markovnikov-type regioselectivity. The stereoselectivity depends on several factors 184... 

The benzylic free radical produced by the addition of the carbamoyl radical to the ethyl cinnamate molecule is more stable than the alternative radical alpha to the ester group. With such an orientation of addition to the a,p-unsaturated ester, this reaction should lead to derivatives of malonic acid. However, it has been found that the intermediate radical, being a stable benzylic free radical, fails to perform the subsequent abstraction of a hydrogen atom from formamide, and thus no chain-transfer step takes place. Instead of performing this step it favours the combination with a semi-pinacol radical, which is present in solution, to yield the hydroxy ester which subsequently lactonizes to give the major product of the reaction (67). 

Cognate preparations. Phenylpropynoic acid. Place a solution of 88 g (84 ml, 0.5 mol) of ethyl cinnamate (Expt 6.137) in 50 ml of carbon tetrachloride in a 500-ml round-bottomed flask. Immerse the flask in ice and add 80 g (25.5 ml, 0.5 mol) of bromine from a separatory funnel slowly with frequent shaking. The halogen will disappear rapidly at first, but more slowly towards the end of the reaction no hydrogen bromide is evolved and the time of the addition is about 20-25 minutes. Allow the mixture to stand for 1 hour, pour the solution into a large evaporating dish and permit the excess of bromine and the carbon tetrachloride to evaporate spontaneously in the fume cupboard. The crude ethyl 2,3-dibromo-3-phenylpropanoate will remain as a solid cake this... 

The C-C double bonds conjugated with carboxyl functions are usually much more readily hydrogenated than usual olefinic bonds, especially with nickel and palladium catalysts. Ethyl cinnamate is rapidly hydrogenated over Raney Ni under mild conditions (eq. 3.19).115 It is also hydrogenated over palladium oxide much faster (eq. 3.20) than over platinum oxide with which 2.9 h were required under the same conditions.5 Cinnamic acid was hydrogenated smoothly to dihydocinnamic acid as the sodium salt over Urushibara Ni in water under ordinary conditions (eq. 3.21).116... 

High catalytic activities, with turnovers of up to 9(X) cycles min , is displayed in the transfer hydrogenation of a,p-unsaturated ketones, such as benzylideneacetone and chalcone, using 2-propanol and catalytic amounts of [Ir(3,4,7,8-Me4-phen)COD]Cl (phen = 1,10-phenanthroline COD = 1,5-cyclo-octadiene) in a weakly alkaline medium. Other Ir-chelated complexes are also active catalysts in this reaction, with over 95% selectivity for the 1,4-reduction mode. Divalent lanthanide derivatives, such as Sml2 or Ybh in stoichiometric quantities, in THF and t-butyl alcohol or methanol reduce ethyl cinnamate and cinnamic acid to give the saturated derivatives. " Similarly, 3-methylcyclohexenone is reduced to 3-methylcyclohexen-l-ol in 67% yield, but a,p-unsaturated aldehydes are nonselectively reduced with these systems. 

The catalytic activity of a powder catalyst should be proportional to its surface area in case its entire surface is equally effectii-e for the catalytic reaction. On the other hand, this correlation does not apply to catalysts whose active sites are located at crystallographically exceptional positions such as edges and corners of its microcrystallies. Schwab and Rudoloph (99) studied as early as 1934 the Topochemistry in Heterogeneous Catalysis, and concluded that the active sites of several catalysts were located at crystal boundaries in their surfaces. The chief evidence represented by these workers is that in various catalytic reactions, e.g., in the hydrogenation of ethyl cinnamate over different specimens of powdered nickel catalysts, the rates are proportional to a power of the catalyst surface areas lying between 1.8 and 4.0. 

The addition of benzoquinone led to the development of more active reoxidation systems. A substoichiometric amount is sufficient when rerr-bntyl hydroperoxide is present as a cooxidant, leading to TONs of up to 280 in the reaction of benzene with ethyl cinnamate (Figure 4.6) [ 14]. Under these conditions, the reaction was found to be applicable to various arenes in combination with several electron-deficient alkenes. Hydrogen peroxide was also found to be a suitable co-oxidant, although the resulting environmentally benign protocol, in which water is formed as the only by-product, gave lower turnover (TON = 35). 

Fujiwara and coworkers [23] extensively studied the phenylation of ethyl cinnamate (28) to produce ethyl 3-phenylcinnamate (29) in the presence of catalytic Pd(OAc)2 using a variety of oxidants, such as silver benzoate, manganese dioxide, 30% hydrogen peroxide, rerr-butyl hydrogen peroxide and the combination of rcrr-butyl hydrogen peroxide and... 

In their communication, however, the authors only reported overall yields of photoproducts, and no kinetic or binding data are available to characterize the intervention of the supramolecular assembly during the photocycloaddition step. In this regard, the choice of ethyl cinnamate as a model compound is also unfortunate, as it cannot be ruled out that the enhancement in yield results from an increase in the single state hfetime of the cinnamate chromophore due to hindered ,Z-isomerization. Although the observed products are the P- and 5-truxinate dimers, which are usually the major products from solution photodimerization, the presence of methylene tethers of different lengths could, in principle, be used to provide evidence for the proposed hydrogen-bonded assembly. 

Cinnamic acid can be readily esterified by the Fischer-Speier method without any risk of the addition of hydrogen chloride at the double bond. Proceed precisely as for the preparation of ethyl benzoate (p. 104), using 20 g. of cinnamic acid and 20 ml. of rectified spirit. When the crude product is poured into water, a sharp separation of the ester is not readily obtained, and hence the addition of about 10 ml. of carbon tetrachloride is particularly desirable. Finally distil off the carbon... 

Ethyl /3-phenyl-/3-hydroxypropionate has been prepared by esterification of /3-phenyl-/3-hydroxypropionic acid obtained by the addition of hydrogen bromide to cinnamic acid and subsequent hydrolysis.1,2 The procedure given is based on that of Andrijewski 3 and of Blaise and Herman.4... 

By using condensing agents which are not at the same time dehydrating agents, the intermediate aldol compound can be isolated (see p. 101). A mixture of acetaldehyde and benzaldehyde yields cinnamic aldehyde by the action of hydrogen chloride, sodium hydrate, or sodium ethylate. (B., 17, 2117 20, 657.)... 

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