Acetaldehyde, photolysis

Fig, 6. The dependence of the product quantum yields of acetaldehyde photolysis on iodine pressure at 60 °C. (Blacet and Loeffler )... 

DEPENDENCE OF PRIMARY QUANTUM YIELDS OF ACETALDEHYDE PHOTOLYSIS ON... 

First quantitative studies of the acetaldehyde photolysis were carried out by Leermakers, at 3130 A, between room temperature and 310 °C. The aldehyde pressure was varied 14 fold, and the light intensity 12 fold. The rate expression was given as... 

THE RELATIVE MOLE NUMBERS OF THE PRODUCTS (REFERRED TO 1 MOLE OF CO) IN THE ACETALDEHYDE PHOTOLYSIS ... 

Dodd , as well as Ausloos and Steacie applied relation (35) to the experimental results of acetaldehyde photolysis. The data obtained at high temperatures seem to fit the Arrhenius straight line derived from the azomethane-acetaldehyde and di-/-butyl peroxide-acetaldehyde systems. At low temperatures, however, considerable deviation from this line could be observed, the possible result of additional methane producing reactions of some sort. According to Dodd, these processes could be (i) primary process II, (//) disproportionation reaction (26) and (in) the wall reaction of the methyl radicals. 

Horowitz, A., and J. G. Calvert (1982). Wavelength dependence of the primary processes in acetaldehyde photolysis. J. Phys. Chem. 86, 3105-3114. 

Horowitz, A., Calvert, J.G. Wavelength dependence of the quantum efficiencies of the primary processes in formaldehyde photolysis at 25°C. Int. J. Chem. Kinet. 10, 805-819 (1978) Horowitz, A., Calvert, J.G. Wavelength dependence of the primary processes in acetaldehyde photolysis. J. Phys. Chem. 86, 3105-3114 (1982)... 

Bacher et al. (2001) and Magneron et al. (2005) have studied the photodecomposition of 2-hydroxyethanal in air. Bacher et al. (2001) employed 240-400nm radiation from a filtered xenon lamp. Their data suggested that process (I) is the major photodecomposition mode, analogous to the bond cleavage seen in acetaldehyde photolysis, although some CH3OH was detected also, presumably via reaction (III). 

No cluster fragmentation was observed initially, although long term photolysis (313 nm) of B in CO saturated cyclohexane eventually did lead to fragmentation to Ru(C0)5 plus acetaldehyde ... 

Irradiation of an alcoholic solution of the antitubercular drug isoniazid (261) with a low-pressure mercury lamp by Ninomiya and Yamamoto gave isolated yields of the hydrazone (262, 60%) and the hydrazide (264, 17%). Nicotinic and picolinic acid hydrazides reacted similarly, as did other alcohols. The production of (262) was easily understood since it was known that photolysis of ethanol gave acetaldehyde which would react spontaneously with the... 

The cyclohexanone postulated in this scheme should also be photoactive. The series of reactions necessary to produce the acetic acid observed [11] is indeed long but currently the only reasonable explanation of this product. Previous investigators [20, 21] had not reported acetic acid from the photolysis of PET even though they isolated acetaldehyde, although Day and Wiles [25] did report it. Thus, one may reasonably assume that the presence of 1,4-cyclohexandimethanol most likely is required to produce acetic acid, at least in significant amounts. 

Photolytic. Dalapon (free acid) is subject to photodegradation. When an aqueous solution (0.25 M) was irradiated with UV light at 253.7 nm at 49 °C, 70% degraded in 7 h. Pyruvic acid is formed which is subsequently decarboxylated to acetaldehyde, carbon dioxide, and small quantities of 1,1-dichloroethane (2-4%) and a water-insoluble polymer (Kenaga, 1974). The photolysis of an aqueous solution of dalapon (free acid) by UV light (X = 2537 A) yielded chloride ions, carbon dioxide, carbon monoxide, and methyl chloride at quantum yields of 0.29, 0.10, 0.02, and 0.02, respectively (Baxter and Johnston, 1968). 

Photolysis of 59a in alcohols (ethanol or isopropanol) gave the corresponding indole 62 (R = H), by reductive diazo cleavage, together with acetaldehyde or acetone (66LA17). 

One such reaction in smog formation is the formation of the acetyl radical such as by sunlight photolysis of acetaldehyde... 

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... 

To illustrate the application of Eqs. (OO) and (PP), let us calculate the rate of photolysis of acetaldehyde. Aldehydes such as CH3CHO play an important role in tropospheric chemistry because they photodissociate to produce free radicals. In the case of acetaldehyde, there are four possible sets of products ... 

Once the actinic fluxes, quantum yields, and absorption cross sections have been summarized as in Table 3.19, the individual products < .,v(A)wavelength interval can be calculated and summed to give kp. Note that the individual reaction channels (9a) and (9b) are calculated separately and then added to get the total photolysis rate constant for the photolysis of acetaldehyde. However, the rate constants for the individual channels are also useful in that (9a) produces free radicals that will participate directly in the NO to N02 conversion and hence in the formation of 03, etc., while (9b) produces relatively unreactive stable products. 

As described in Chapter 5, the natural lifetime for acetaldehyde with respect to photolysis under these conditions can be calculated from kp for the overall reaction. The natural lifetime, t, is defined as the time for the concentration of CH3CHO to fall to 1/e of its initial value, where e is the base of natural logarithms. The natural lifetime of acetaldehyde under these conditions is therefore given by r = 1 /kp = 5.5 X 106 s = 63 days. Of course, these conditions do not exist for 63 days, so the lifetime is hypothetical. However, it does provide a sort of back-of the envelope method of assessing the relative rapidity of loss of the compound by photolysis compared to other processes, such as reaction with OH. 

A thin-walled glass tube containing acetaldehyde (0.5 mL) and (f-BuO)2 (3 pL) was degassed by two freeze -thaw cycles and frozen in liquid N2. To this was vacuum transferred [1.1. IJpropellane (6-7 mg). The tube was sealed under vacuum, warmed to rt, and photolyzed for 15 min in a Rayonet style photolysis apparatus. The tube was broken open and the excess acetaldehyde allowed to evaporate at rt, leaving solid material. The solid was chromatographed (silica gel, pentane/Et20 5 1) to give the product, yield 8.4 mg (52%). 

Different results were reported for the photolysis of dihydro-1,2,4,5-tetrazines. 3,6-Diphenyl-l,4-dihydro-l,2,4,5-tetrazine (80) afforded 3,5-diphenyl-l,2,4-triazole (124) on photolysis (70T2619,69JOC199), while the 3,6-dimethyl-1,6-dihydro compound (125) yielded acetaldehyde azine (126) and nitrogen on photolysis, as in the thermolysis reaction (72HCA1404). 

The ability of ethylene oxide to undergo rearrangement to acetaldehyde was mentioned (see section. L2.) in connexion with the thermal decomposition and photolysis of ethylene oxide, and also (see section m.l.C.) in connexion with catalytic ethylene oxidation at elevated temperatures. This characteristic property is discussed, again below with regard, to reactions of epoxides with Qrignard reagents (see section IV.4.F,). For the purposes of this section the subject of epoxide isomerization can be divided into two parts. The first, and most extensive, is concerned with thermal and acid-catalyzed ethylene oxide isomerisation the second involves base-catalyzed rearrangement. 

In processes I and II, the acetyl and methyl radicals react with solvent molecules giving respectively acetaldehyde and methane. In the third process chain degradation occurs followed eventually by disproportionation. Evidently the same photolysis carried out in the presence of a second monomer (acrylonitrile yields graft copolymers (I and II) and, possibly, some block copolymers (III), together with homopolymer initiated by the methyl and acetyl radicals. The formation of graft copolymers seems more likely on account of the greater stability of the radicals produced in reaction schemes I and II compared to scheme III. 

Recombination of various radical species formed during photolysis of water and methane yield acetaldehyde (equation 8.39), methanol (equation 8.40), and other organic species [10,13] ... 

The photolysis of acetaldehyde has been shown to involve three primary processes. 

Ethylene oxide (C2H40) and acetaldehyde (CH3CHO) were found as main products. CO was also detected. Figure 2 shows the time dependence of these three products. The yield of C2H40 increases linearly with time, which indicates that C2H40 does not react to any appreciable extent through secondary reactions or subsequent photolysis. The yield of... 

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