Aldehydes decomposition

Two parallel photolytic reactions of aldehydes decomposition are known [205] ... 

Eqn. (2) seems to be generally suitable for describing the initial rate of priopion-aldehyde decomposition. According to this equation, the reaction order approaches f at high pressures and low temperatures. (Note the activation energies )... 

Reduced nickel is a much more active catalyst than copper toward the dehydrogenation of ethanol. At 250° C. reaction is pronounced, but even at this low temperature nickel is a powerful catalyst for aldehyde decomposition ... 

This is shown by the facts that the aldehyde-hydrogen ratio is only 35.7 per cent and the gas composition shows 60 per cent hydrogen, 20 per cent carbon monoxide, and 15-17 per cent methane. The presence of 8 per cent water in the ethanol apparently has no protective effect on the aldehyde as it does in the presence of copper catalysts." Because of this undesirable activity in promoting aldehyde decomposition, nickel catalysts are not applicable to the dehydrogenation of ethanol or alcohols in general. 

Alumina having strong catalytic action may be prepared by precipitating the aluminum from a one to two per cent aluminum nitrate solution with dilute ammonia. The precipitate is washed by decantation six times, washed on the filter several times, dried over phosphorous pentoxide for 24 hours, heated in an air oven at 240° C., and ground to pass a 200 mesh sieve. After operating for five hours at a temperature close to 500° C. this catalyst showed but a slight decrease in activity.84 An 80 per cent yield of 98 per cent ethylene was obtained from absolute alcohol at 490° C. When water and alcohol were passed in together somewhat more aldehyde decomposition was obtained. 

Metal catalysts, other than iron, which are known to promote aldehyde decomposition at ordinary pressures exhibit in different degrees the same variations that have just been described when the heating of the substance is conducted under pressure. In general, it may be saitl that the equilibrium which is established at any given temperature and pressure is to some extent independent of the substance which is used as tine starting point of the reaction, since when acetaldehyde is substituted for alcohol, the same gaseous decomposition products are formed in the same relative amounts and the liquid products likewise always consist of aldehyde, alcohol, water, saturated and unsaturated hydrocarbons. 

Various explanations have been offered for the mechanism of the formation of the carbon dioxide and of the ethane which has also been obtained in certain cases. None of these are entirely free from objections. Aldehydes are known to condense to esters under certain conditions and the decarboxylation of such has been offered as one explanation. However, the presence of carbon dioxide by this mechanism has not been supported by the evidence of other products of ester decomposition. Methane formation has not been reported in all cases where carbon dioxide has been found and this, together with the fact that entirely inadequate amounts of carbon have been found, seems to point that the rupture of acetaldehyde to C -+- C02 instead of carbon monoxide does not occur. The decomposition of aldehyde alone in the presence of precipitated iron oxide at 400° C. gave 40 per cent carbon dioxide and a large quantity of resinous matter.70 In the presence of reduced nickel, however, no carbon dioxide was formed and no resinous matter or oil resulted although nickel is an active catalyst for aldehyde decomposition. 

Oenanthal n. Aldehyde decomposition product derived during the dehydration of castor oil. 

For formaldehyde oxidation, 20 wt% Mo/WC prepared by CVD with metal hexacarbonyl precursors showed a current density of 4 x 10 A/m at 0.3 V (vs RHE) and 323 K, whereas pure WC electrode showed 1.2 x 10 A/m (159). According to this report, the electrochemical activities could be enhanced because Mo might act as the center for removal of poisonous species and provide other pathways of aldehyde decomposition. 

A modification to the alkene ozonolysis reaction employs dimethyl sulphide to reduce the ozonide to a keto-aldehyde. Decomposition of benzoyl poroxide is accelerated by aliphatic sulphides or disulphides, owing to nucleophilic attack by sulphur at oxygen. An extension of work described in 1%9 by the same authors showing the ability of sulphides and thiols to quench pffioto-excited benzophenone has been described. ... 

Dinitrophenylhydra2ones usually separate in well-formed crystals. These can be filtered at the pump, washed with a diluted sample of the acid in the reagent used, then with water, and then (when the solubility allows) with a small quantity of ethanol the dried specimen is then usually pure. It should, however, be recrystallised from a suitable solvent, a process which can usually be carried out with the dinitrophenylhydrazones of the simpler aldehydes and ketones. Many other hydrazones have a very low solubility in most solvents, and a recrystallisation which involves prolonged boiling with a large volume of solvent may be accompanied by partial decomposition, and with the ultimate deposition of a sample less pure than the above washed, dried and unrecrystal-lised sample. 

Note. The 2,4-dinitrophenylhydrazones of many higher aldehydes and ketones may be insoluble in most solvents. In this case, Mter them off, wash with ethanol, dry and take the m.p. attempted recrystallisation may cause partial decomposition. (M.ps., pp. 530-540.)... 

Aromatic aldehydes usually have relatively high boiling points, but distil with little or no decomposition. The vapours burn with a smoky flame. They are easily oxidised on standing in the air into the corresponding acids the odours are often pleasant and characteristic. Aromatic aldehydes, by virtue of their high molecular weight, yield... 

The decomposition of a glycidic ester to an aldehyde and carbon dioxide may involve the formation of a quasi six-membered ring, followed by the shift of three electron pairs ... 

The limitations of this reagent are several. It caimot be used to replace a single unactivated halogen atom with the exception of the chloromethyl ether (eq. 5) to form difluoromethyl fluoromethyl ether [461 -63-2]. It also caimot be used to replace a halogen attached to a carbon—carbon double bond. Fluorination of functional group compounds, eg, esters, sulfides, ketones, acids, and aldehydes, produces decomposition products caused by scission of the carbon chains. 

Okfm Syntheses. Conversion of aldehydes and ketones to olefins by the base-catalyzed decomposition of -toluenesulfonic (Ts) acid hydrazones (10) is known as the Bamford-Stevens reaction (54,55). 

Browning Reactions. The fluorescent components formed in the browning reaction (8) of peroxidized phosphatidylethanolamine are produced mainly by interaction of the amine group of PE and saturated aldehydes produced through the decomposition of fatty acid hydroperoxides. 

Dioxetanones decompose near or below room temperature to aldehydes or ketones (56). The decomposition reactions are weakly chemiluminescent Qc ca 10 ein/mol) because the products are poorly fluorescent. However, addition of 10 M mbrene provides 2iQc ca 10 ein/mol, and 2iQc on the order of was calculated at mbrene concentrations above 10 M after correcting for yield loss factors (57). The decomposition rates are first order ia... 

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

Decomposition products from primary and secondary dialkyl peroxides include aldehydes, ketones, alcohols, hydrogen, hydrocarbons, carbon monoxide, and carbon dioxide (44). 

Thermal decomposition of dihydroperoxides results in initial homolysis of an oxygen—oxygen bond foUowed by carbon—oxygen and carbon—carbon bond cleavages to yield mixtures of carbonyl compounds (ketones, aldehydes), esters, carboxyHc acids, hydrocarbons, and hydrogen peroxide. 

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