Hydrogen of ethanol

Figure 1.11 Enantiotopic groups. Top, enantiopic carboxymethyl groups of citric acid, showing their enantiomeric environments, and enantiopic hydrogens of ethanol, showing their proR and proS environments.

Oxygen and the two carbons are connected in the order CCO in ethanol and COC In dimethyl ether. The connectivity and the fact that carbon normally has four bonds In neutral molecules allow us to place the hydrogens of ethanol and dimethyl ether. 

Scheme 8.11. A cartoon representation of the oxidation of ethanol (ethyl alcohol, CH3CH2OH) to ethanal (acetaldehyde, CH3CHO) with the cofactor nicotmamide adenine dinucleotide (NAD ).The curved arrows depict the loss of the pro-R C-1 hydrogen from the former as it is being added to the re-face of the latter. The reverse reaction, loss of the C-4 pro-R hydrogen from NADH to ethanal (acetaldehyde, CH3CHO), where it becomes the pro-R hydrogen of ethanol (ethyl alcohol, CH3CH2OH), is indicated by the arrows connecting the structures on the right and left. It is important to note that it is the same hydrogen removed in the oxidation process and which is returned in the reduction process.

WORKED PROBLEM 16.30 (a) Each methylene hydrogen of ethanol can be replaced by deuterium to give a pair of chiral deuterioethanols. Show this process and indicate which of the new compounds is (R) and which is (S). (b) Oxidation of (R)-Tdeuterioethanol produces deuterio-NADH (NADD) and acetaldehyde. Predict the products of the oxidation of (i)-l-deuterioethanol with NAD. Explain carefully. 

If the mixture contains an excess of ethanol, and is heated to 140°, the ethyl hydrogen sulphate reacts with the ethanol, giving diethyl ether And regenerating the sulphuric acid ... 

CH3COOH + HOC2H5 - CH3GOOC2H3 + H2O If, however, concentrated sulphuric acid is present, the water is absorbed, the back reaction prevented, and a high yield of ethyl acetate is obtained. In practice the reaction is not so simple. It was formerly supposed that, since the sulphuric acid is usually added to the alcohol, ethyl hydrogen sulphate and water are formed, the latter being absorbed by the excess of sulphuric acid, A mixture of ethanol and acetic acid is then added to the ethyl hydrogen sulphate,... 

Place 20 g. of benzoic acid and 20 ml. (16 g.) of ethanol in A, connect up the apparatus, and then heat the flask on a sand-bath so that the solution in the flask boils gently. At the same time, pass a brisk current of hydrogen chloride into the reaction... 

Isopropanol has been used in the above experiment because it gives a greater yield of the phosphite than ethanol gives of diethyl hydrogen phosphite. The latter, b.p. 74 /i4 mm., can be prepared by replacing the isopropanol in the above experiment by 29 ml. (23 g.) of ethanol. 

Cool the filtrate (A) to 5-10° and add concentrated hydrochloric acid dropwise and with vigorous stirring (FUME CUPBOARD hydrogen cyanide is evolved) to a pH of 1-2 (about 50 ml.) a crude, slightly pink 3-indoleacetic acid is precipitated. The yield of crude acid, m.p. 159-161°, is 20 g. Recrystallise from ethylene dichloride containing a small amount of ethanol 17 -5 g. of pure 3 indoleacetic acid, m.p. 167-168°, are obtained. 

Schatzmann, in 1891, tried to prepare 2-thiazolines by hydrogenation of thiazoles and by the action of sodium and ethanol on 2,4-dimethyl-thiazole, 2-methylthiazole, and 2-methyl-4-phenylthiazole (476). None of these substrates was reduced to thiazoline the second gave no reaction and the first underwent ring cleavage, leading to a mixture of n-propylmercaptan and ethylamine (Scheme 90). Three years later the same... 

On being heated with a solution of sodium ethoxide in ethanol compound A (CyHisBr) yielded a mixture of two alkenes B and C each having the molecular formula C7H14 Catalytic hydrogenation of the major isomer B or the minor isomer C gave only 3 ethylpentane Suggest structures for compounds A B and C consistent with these observations... 

Compound A (C7Hi5Br) is not a primary alkyl bromide It yields a single alkene (compound B) on being heated with sodium ethoxide in ethanol Hydrogenation of compound B yields 2 4 dimethylpentane Identify compounds A and B... 

According to the proposed mechanism for biological 0x1 dation of ethanol the hydrogen that is transferred to the coenzyme comes from C 1 of ethanol Therefore the dihydropyridme ring will bear no deuterium atoms when CD3CH2OH IS oxidized because all the deuterium atoms of the alcohol are attached to C 2... 

Reduction. Acetaldehyde is readily reduced to ethanol (qv). Suitable catalysts for vapor-phase hydrogenation of acetaldehyde are supported nickel (42) and copper oxide (43). The kinetics of the hydrogenation of acetaldehyde over a commercial nickel catalyst have been studied (44). 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

Hydrogenation of Acetaldehyde. Acetaldehyde made from acetylene can be hydrogenated to ethanol with the aid of a supported nickel catalyst at 150°C (156). A large excess of hydrogen containing 0.3% of oxygen is recommended to reduce the formation of ethyl ether. Anhydrous ethanol has also been made by hydrogenating acetaldehyde over a copper-on-pumice catalyst (157). 

Synthesis Ga.s, Since petroleum prices rose abmpdy in 1974, the production of ethanol from synthesis gas, a mixture of carbon monoxide and hydrogen, has received considerable attention. The use of synthesis gas as a base raw material has the same drawback as fermentation technology low yields limited by stoichiometry. 

Ethylamines. Mono-, di-, and triethylamines, produced by catalytic reaction of ethanol with ammonia (330), are a significant outlet for ethanol. The vapor-phase continuous process takes place at 1.38 MPa (13.6 atm) and 150—220°C over a nickel catalyst supported on alumina, siUca, or sihca—alumina. In this reductive amination under a hydrogen atmosphere, the ratio of the mono-, di-, and triethylamine product can be controlled by recycling the unwanted products. Other catalysts used include phosphoric acid and derivatives, copper and iron chlorides, sulfates, and oxides in the presence of acids or alkaline salts (331). Piperidine can be ethylated with ethanol in the presence of Raney nickel catalyst at 200°C and 10.3 MPa (102 atm), to give W-ethylpiperidine [766-09-6] (332). 

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