Volatile aldehydes

This procedure is representative of a new general method for the preparation of noncyclic acyloins by thiazol ium-catalyzed dimerization of aldehydes in the presence of weak bases (Table I). The advantages of this method over the classical reductive coupling of esters or the modern variation in which the intermediate enediolate is trapped by silylation, are the simplicity of the procedure, the inexpensive materials used, and the purity of the products obtained. For volatile aldehydes such as acetaldehyde and propionaldehyde the reaction Is conducted without solvent in a small, heated autoclave. With the exception of furoin the preparation of benzoins from aromatic aldehydes is best carried out with a different thiazolium catalyst bearing an N-methyl or N-ethyl substituent, instead of the N-benzyl group. Benzoins have usually been prepared by cyanide-catalyzed condensation of aromatic and heterocyclic aldehydes.Unsymnetrical acyloins may be obtained by thiazol1um-catalyzed cross-condensation of two different aldehydes. -1 The thiazolium ion-catalyzed cyclization of 1,5-dialdehydes to cyclic acyloins has been reported. 

The dioxolanones 33 <95JAP07291959> and 34 <95JAP07285960> are both reported to be useful as solvents, while 35 has been used as an X-ray contrast medium <96MIP19487>. Carboxydioxolanes such as 36 are useful for controlled release of volatile aldehyde pheromones <96JCR(S)274> and pharmaceutically active amines R2NH can be administered in... 

In the vast majority of gas-solid reactions, gaseous or evaporated compounds react at the surface of a solid catalyst. These catalytic processes are very frequently used in the manufacture of bulk chemicals. They are much less popular in processing of the large molecules typical of fine chemistry. These molecules are usually thermally sensitive and as such they will at least partially decompose upon evaporation. Only thermally stable compounds can be dealt with in gas-solid catalytic processes. Examples in fine chemicals manufacture are gas-phase catalytic aminations of volatile aldehydes, alcohols, and ketones with ammonia, with hydrogen as... 

Both male and female coyotes, C. latrans, are attracted to volatile aldehydes from sheep liver and estrous urine of female coyotes. The most active compoimds were octanal, nonanal, decanal, and imdecanal. The aldehydes released sniffing and rub-rolling, but little lick-chewing and biting. Therefore, these compoimds are better suited to attract coyotes to traps than to toxicant-delivery systems that rely on the latter behaviors (Scrivnereta/., 1984). 

Early electrochemical processes for the oxidation of alcohols to ketones or carboxylic acids used platinum or lead dioxide anodes, usually with dilute sulphuric acid as electrolyte. A divided cell is only necessary in the oxidation of primary alcohols to carboxylic acids if (he substrate possesses an unsaturated function, which could be reduced at the cathode [1,2]. Lead dioxide is the better anode material and satisfactory yields of the carboxylic acid have been obtained from oxidation of primary alcohols up to hexanol [3]. Aldehydes are intermediates in these reactions. Volatile aldehydes can be removed from the electrochemical cell in a... 

This procedure is to be avoided with steam-volatile aldehydes (e.g., p-chlorobenzaldehyde) in which case the reduction product is isolated by solvent extraction.4... 

In a first reactor, where benzoylformate decarboxylase (BFD) is retained, benz-aldehyde and acetaldehyde are coupled to yield (S)-hydroxy-l-phenylpropanone. This hydroxy ketone is then reduced to the corresponding diol in a second reactor by an alcohol dehydrogenase (ADH). Regeneration of the necessary cofactor is achieved by formate dehydrogenase (FDH) or by other methods. To avoid additional consumption of redox equivalents by unselective reduction of residual starting material from the first reactor, the volatile aldehydes are removed via an inline stripping module between the two membrane reactors. In this setup the diol was produced with high optical purity (ee, de > 90%) at an overall space-time yield of 32 g L d . ... 

The volatiles produced by the LOX pathway and autoxidation are typically volatile aldehydes and alcohols responsible for fresh and green sensorial notes. In the LOX pathway these volatile compounds are produced in response to stress, during ripening or after damage of the plant tissue. The pathway is illustrated in Scheme 7.2. Precursors of the LOX (EC 1.13.11.12) catalysed reactions are Cis-polyunsaturated fatty acids with a (Z,Z)-l,4-pentadiene moiety such as linoleic and a-linolenic acids that are typically oxidised into 9-, 10- or 13-hydro-peroxides depending on the specificity of the LOX catalyst. These compounds are then cleaved by hydroperoxide lyase (HPL) into mainly C, C9 and Cio aldehydes, which can then be reduced into the corresponding alcohols by alcohol dehydrogenase (ADH EC 1.1.1.1) (Scheme 7.2) [21, 22]. The production of volatile compounds by the LOX pathway depends, however, on the plants as they have different sets of enzymes, pH in the cells, fatty acid composition of cell walls, etc. 

More than 350 volatile compounds have been identified in apples [44]. Only a few of these volatiles have been identified as being responsible for apple aroma [45]. The most abundant volatile components in apples are esters (78-92% of total volatiles), alcohols (6-16% of total volatiles), aldehydes, ketones and ethers [35, 45], which are present in various amounts in different cultivars [46]. Esters are the principal compounds responsible for apple odour (Table 7.1, Fig 7.1)... 

This simple method of heads disposal by refermentation eliminated the earlier deterrent to taking an adequate cut to control volatile aldehydes to the desired level, now considered to be approximately 10 ppm or less in new brandy distillates. 

See Section 15-6B useful for the preparation of volatile aldehydes because with these, further oxidation usually can be prevented by distilling the product out of the reaction mixture. 

In simple molecules, it is possible to obtain a good yield of aldehyde— including examples possessing an important proportion of hydrate in equilibrium—by continuous distillation of the aldehyde from the reaction mixture.73 This procedure only succeeds in the preparation of simple volatile aldehydes. 

The 60 per cent sulfuric acid is chosen as a wash liquid because it is miscible with butyl alcohol but not with the ester. The volatile aldehyde disappears in the two fractionations, while the butyric acid is removed by the alkali. 

Use of GLC to determine qualitative and quantitative composition of volatile compounds in citrus oils has become common. However, there are many discrepancies in the literature concerning the quantitative composition of citrus oils. Analyses of volatile aldehydes are of major importance, because composition and quantity of these compounds influence the quality and value of citrus oils. Compositional differences between... 

Comparison of (5) with (6a) + (6b) (heated in separate tubes but smelled together) should show similarly the extent to which furfural can affect a normal aldehyde. Comparison of (7) with (8a) + (8b) and of (9) with (10a) + (10b) should show little difference because of considerable survival of volatile aldehydes in presence of a blocking Group 2 aldehyde (from ile). 

Adhesives - Short term method for measuring the emissions properties of low-solvent or solvent-free adhesives after application. Part 3 Determination of volatile aldehydes. 

Scheme 13.2 Auto-oxidation of linolenic acid (truncated) leading to radical propagation, intermolecular cross-linking, and volatile aldehyde emissions.

Wang, Springs and Morrison (2005) showed that countertops that become coated with cooking oils or soaps will generate volatile aldehydes in the presence of ozone, in chemistry akin to Scheme 13.6. They verified in field studies (Wang and Morrison, 2006) that kitchen counters are a major emitter of secondary aldehydes (on a unit area basis). 

Jalliffier-Merlon, E., J. C. Marty, V. Denant, and A. Saliot. 1991. Phytoplankton sources of volatile aldehydes in the river Rhone estuary. Estuarine Coastal and Shelf Science 32 463-482. 

Chemical reactions occur during microwave processing of food systems, however, their contribution to flavor appears to be minimal. The volatile aldehydes quickly flash off during subsequent heating. The desirable baked, toasted, and roasted flavors typical of Maillard Browning do not develop in microwave heated food products. 

The oxidation of primary alcohols with K2Cr207 in aqueous solution to nothing but the aldehyde, (i.e., without further oxidation to the carboxylic acid) is possible only if a volatile aldehyde results and is distilled off as it is formed. This is the only way to prevent the further oxidation of the aldehyde in the (aqueous) reaction mixture. Selective oxidations of primary alcohols to aldehydes with the Jones reagent succeed only for allylic and benzylic alcohols. Otherwise, the Jones reagent directly converts alcohols into carboxylic acids (see above). 

Levrand, B. and Herrmann, A. (2007) Controlled light-induced release of volatile aldehydes and ketones by photofragmentation of 2-oxo-(2-phenyl) acetates. Chimia, 61, 661-664. 

Jenq, W. R., Bassette, R., and Crang, R. E. (1988). Effects of light and copper ions on volatile aldehydes of milk and milk fractions. J. Dairy Sci. 71, 2366-2372. 

---