Acetaldehyde, from ethanol

Calcium carbide can be treated with water to produce acetjiene from which other organic compounds, eg, ethanol, acetaldehyde, may be obtained (6) (see... 

Cyclopentadiene itself has been used as a feedstock for carbon fiber manufacture (76). Cyclopentadiene is also a component of supported metallocene—alumoxane polymerization catalysts in the preparation of syndiotactic polyolefins (77), as a nickel or iron complex in the production of methanol and ethanol from synthesis gas (78), and as Group VIII metal complexes for the production of acetaldehyde from methanol and synthesis gas (79). 

Direct Hydration of Ethylene. Hydration of ethylene to ethanol via a Hquid-phase process cataly2ed by dilute sulfuric acid was first demonstrated more than a hundred years ago (82). In 1923, the passage of an ethylene-steam mixture over alumina at 300°C was found to give a small yield of acetaldehyde, and it was inferred that this was produced via ethanol (83). Since the late 1920s, several industrial concerns have expressed interest in producing ethanol synthetically from ethylene over soHd catalysts. However, not until 1947 was the first commercial plant for the manufacture of ethanol by catalytic hydration started in the United States by Shell the same process was commerciali2ed in the United Kingdom in 1951. 

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out ia the vapor phase over a silver or copper catalyst (305). Conversion is slightly over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively cataly2es the Uquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place ia the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and Uquid-phase oxidation of ethanol have been described ia the Uterature (307,308). 

In a similar manner, ethanol can be oxidized by the dichromate ion to form a compound called acetaldehyde, CHaCHO. The molecular structure of acetaldehyde, which is similar to that of formaldehyde, is shown at the bottom in Figure 18-6. We see that the molecule is structurally similar to formaldehyde. The methyl group, —CH3, replaces one of the hydrogens of formaldehyde. The balanced equation for the formation of acetaldehyde from ethanol is... 

Figure 3. Arrhenius plots for the formation of formaldehyde or acetaldehyde from methanol or ethanol, normalized by the number of vanadiums (open symbols) and by the amount of oxygen uptake measured at 625 K (filled symbols). Lines on the right panel are calculated from the data reported by Oyama and Somorjai [11].

Infrared spectroscopy has also been employed to follow the formation of acetaldehyde and acetic acid on Pt during ethanol electro-oxidation. On the basal planes, acetaldehyde could be observed starting at about 0.4 V (vs. RHE), well before the onset of CO oxidation, while the onset of acetic acid formation closely follows CO2 formation [Chang et al., 1990 Xia et al., 1997]. This is readily explained by the fact that both CO oxidation and acetic acid formation require a common adsorbed co-reactant, OHads, whereas the formation of acetaldehyde from ethanol merely involves a relatively simple proton-electron transfer. 

Disulfiram is the generic name for Antabuse, a drug used in the treatment of chronic alcoholism. Disulfiram potentiates the toxic and carcinogenic effects of 1,2-dibromoethane in experimental animals. Presumably, this occurs by blocking conversion of the aldehyde metabolite as with acetaldehyde from ethanol. There is no evidence that similar effects occur in humans. Based on animal data, however, Ayerst Laboratories, producers of Antabuse (disulfiram), recommended the following in the package insert "Patients taking Antabuse tablets should not be exposed to ethylene dibromide or its vapors" (PDR 1991). 

The reaction has been shown to be carried out by a pyravate decarboxylase and involves thiamine pyrophosphate in the formation of activated acetaldehyde from pyravate, which then condenses with benzaldehyde. Evidently, pyravate decarboxylase, a crucial enzyme for ethanol biosynthesis, is nsed in an urmatural way... 

A reaction which could involve the vinyl alcohol tautomer of acetaldehyde is the synthesis of 2-(2-naphthyl)quinoline by photolysis of the anil (393) in ethanol (68TL3685). From the benzaldehyde anil of a-naphthylamine by a similar reaction, 2-phenylbenzo[Jt]quinoline... 

During the production of recovery flavours, apple wines or brandies, the interaction with ethanol, acetaldehyde and acetic acid represents the next level of interactions. The reaction products contain compounds which result from esterification and acetal formation reactions, which are summarised in Table 21.4. 

Table 21.4 Reaction products originating from (2)-3-hexenal, ethanol, acetaldehyde and acetic acid ...

Figure 6 Adsorption isotherms for (a) ethanol and acetaldehyde (from Ref. 49), and (b) toluene (From Ref. 50) on TiOi.

The enthalpy changes for adsorption of acetaldehyde (step 3), ethanol (step 5), hydrogen (step 6), water (step 8), and acetic acid to form adsorbed acetate (step 9) were adjusted in the reaction kinetics analysis. The initial estimates of the heats of adsorption of acetaldehyde, ethanol, and hydrogen were obtained from the DFT predictions for these species on Cu(211) (Table VIII). The heat of adsorption of water was constrained to be equal to the heat of adsorption of ethanol in these analyses. The steps involving adsorption of ethanol, acetaldehyde, water, and the step in which acetic acid forms the surface acetate species were all assumed to be nonactivated. 

CCSD(T)/6-311++G(d,p)//BHandHLYP/6-311++G(d,p) [169]. The authors found that he ZPE corrected barriers for H abstractions from the alpha position in ethanol and from the aldehydic site in acetaldehyde are 0.2 kcal/mol lower than those corresponding to the equivalent abstractions in glycolaldehyde. This difference is responsible for the decrease in k. In SAR, the deactivation of the -CH2 site by the >G=0 substituent is taken into account by introducing a factor F(>C=0) = 0.75. However, no deactivation is considered for the aldehydic abstraction. This deactivation occurs because of the intramolecular hydrogen bond in OO-s-cis glycolaldehyde, which is a very specific characteristic of this molecule. 

An aqueous solution containing ethyl alcohol in water is fermented to produce dilute acetic acid. The feed mixture (the ethanol solution and the bacteria that make the fermentation occur) and a>r are fed at a temperature Tq. The product solution contains ethanol, acetaldehyde (CH CHO), acetic acid, and water. All liquid and gaseous effluents are at temperature T. The variables involved in the process are n (mol feed solution), x (mol eihanol/mol feed solution), n i (mol air fed). (percent excess air),nah, (gram-moles of ethanol, acetaldehyde, acetic acid, and water, respectively, in the product mixture), Hox, n (gram-moles of oxygen and nitrogen, respectively, emerging from the reactor), 7 , 7, and 0(kJ heat transferred . 

Methyl ketones can be distinguished from other ketones by the iodoform test. The methyl ketone is treated with iodine in a basic solution. Introduction of the first iodine atom increases the acidity of the remaining methyl protons, so halogenation stops only when the triiodo compound has been produced. The base then allows the relatively stable triiodomethyl carban-ion to leave and a subsequent proton transfer gives iodoform, a yellow crystalline solid of mp 119-123°C. The test is also positive for fragments easily oxidized to methyl ketones, such as CH3CHOH— and ethanol. Acetaldehyde also gives a positive test because it is both a methyl ketone and an aldehyde. 

FIGURE 4.72 Plasma concentrations of alcohol and related metabolites after a dose of alcohol. Human subjects received a dose of ethanol via a stomach tube (0.15 g of ethanol/kg body weight). Plasma concentrations of ethanol ( ), acetaldehyde (O), and acetate (A) were measured at the indicated times. Acetaldehyde concentrations were one-thousandth those of ethanol, about 1.0 pM. (Redrawn with permission from DiPadova et ah, 1987.)... 

ADH was isolated and partially purified from orange juice vesicles and examined for substrate specificity, maximum relative velocity (Vr) and affinity (1/Km) (12) Ethanol is the preferred saturated alcohol for reduction to the aldehyde based on Vr and 1/Km. Unsaturated alcohols, 2-propenol, 2-butenol and 2-hexenol, had comparable to or higher Vr s and l/Km s than ethanol. ADH had 5- to 30-fold greater affinity for saturated aldehydes than the corresponding saturated alcohols, whereas affinities of the unsaturated alcohols and aldehydes were similar. The apparent equilibrium constants (Kapp = 0.003 for ethanol - acetaldehyde pair) favor alcohol formation in the saturated series. Other aldehydes compete with acetaldehyde for the enzyme but the concentration of acetaldehyde is much higher than other aldehydes in juice vesicles and the 1/Km for acetaldehyde is 10 X higher than for other aldehydes found in the juice vesicles. 

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