Low molecular weight aldehydes

Many low molecular weight aldehydes and ketones are important industrial chem icals Formaldehyde a starting material for a number of plastics is prepared by oxida tion of methanol over a silver or iron oxide/molybdenum oxide catalyst at elevated temperature... 

The protonated form of poly(vinyl amine) (PVAm—HCl) has two advantages over many cationic polymers high cationic charge densities are possible and the pendent primary amines have high reactivity. It has been appHed in water treatment, paper making, and textiles (qv). The protonated forms modified with low molecular weight aldehydes are usehil as fines and filler retention agents and are in use with recycled fibers. As with all new products, unexpected appHcations, such as in clear antiperspirants, have been found. It is usehil in many metal complexation appHcations (49). 

When catalyzed by acids, low molecular weight aldehydes add to each other to give cyclic acetals, the most common product being the trimer. The cyclic trimer of formaldehyde is called trioxane, and that of acetaldehyde is known as paraldehyde. Under certain conditions, it is possible to get tetramers or dimers. Aldehydes can also polymerize to linear polymers, but here a small amount of water is required to form hemiacetal groups at the ends of the chains. The linear polymer formed from formaldehyde is called paraformaldehyde. Since trimers and polymers of aldehydes are acetals, they are stable to bases but can be hydrolyzed by acids. Because formaldehyde and acetaldehyde have low boiling points, it is often convenient to use them in the form of their trimers or polymers. 

The procedures used to determine ambient carbonyl concentrations involve a collection step with silica or C18 cartridges impregnated with 2,4-dinitrophenylhydrazine. Contamination is inevitable with this system, and blanks must be used to compensate for the degree of contamination. Selection of the appropriate blank values to subtract is a difficult and uncertain process. Consequently, development of a gas chromatographic system that will resolve and respond to the low-molecular-weight aldehydes and ketones is needed. The mercuric oxide and atomic emission detectors should provide adequate response for the carbonyls. 

Bubb WA, Berthon HA, Kuchel P. Tris buffer reactivity with low molecular-weight aldehydes, NMR characterization of the reactions of glyceraldehyde 3-phosphate. Bioorg Chem 1995 23 119-130. 

Low molecular weight aldehydes and ketones are used in the manufacture of resins, dyes, esters, and other organic chemicals. Many ketones including acetone and methyl ethyl ketone are industrial solvents. Some of the compounds that are used commercially are presented in Table 2.1.1. Mary aldehydes and ketones are emitted into the atmosphere from chemical and combustion processes. Photochemical degradation of many organic substances also generates lower aldehydes and ketones. 

Low molecular weight aldehydes and ketones (e.g. formaldehyde and acetone) are soluble in water. This is because the oxygen of the carbonyl group can participate in intermolecular hydrogen bonding with water molecules ... 

Habboush AE, Farroha SM, Naoum OF, et al. 1988. The collection and direct analysis of low molecular weight aldehydes from automobile exhaust gases by GLC. Int J Environ Anal Chem 32 79-85. 

Ogawa I, Fritz JS. 1985. Determination of low concentrations of low-molecular-weight aldehydes and ketonse in aqueous samples. J Chromatogr 329 81-89. 

The second reason that bisulfite compounds are useful is that they are soluble in water. Some small (that is, low molecular weight) aldehydes and ketones are water-soluble—acetone is an example. But most larger (more than four or so carbon atoms) aldehydes and ketones are not. This does not usually matter to most chemists as we often want to carry out reactions in organic solvents rather than water. But it can matter to medicinal chemists, who make compounds that need to be compatible with biological systems. And in one case, the solubility of bisulfite adduct in water is literally vital. 

A stream of nitrogen gas was passed through freshly collected mother s milk and the effluent collected by adsorption on a Tenax TA resin (2,6-diphenylene oxide based). Subsequent desorption into a GC-MS instrument led to the identification of 21 volatile components (low-molecular-weight aldehydes, ketones, alcohols, and lactone) in the milk headspace. When each was screened for behavioral activity, one, 2-methylbut-2-enal (34), was clearly the main compound responsible for eliciting searching—grasping responses in the rabbit pup test subjects. 

Controlled oxidation of a primary alcohol with a mixture of sulfuric and chromic acids gives the corresponding aldehyde. In the preparation of low-molecular-weight aldehydes, an aqueous medium is used and the product is removed by steam distillation, thus preventing further oxidation. This procedure is well illustrated by the preparation of propion-aldehyde (49%) and isovaleraldehyde (60%). Certain benzyl alcohols are dissolved in aqueous acetic acid for chromic acid oxidation. Ole-finic aldehydes are produced by a rapid low-temperature (5-20°) oxidative procedure, as illustrated by the preparation of 2-heptenal (75%) from 2-heptenol. Aldehyde ethers such as methoxyacetaldehyde and ethoxy-acetaldehyde have been prepared by the chromic acid oxidation of the corresponding alcohols in 17% and 10% yields, respectively. ... 

Apart from the environmental factors, chemical compounds also induce cross-linking of gelatin. Supporting this is the mechanism in Fig. 5, which highlights the role of external aldehydes. Among the low molecular weight aldehydes, formaldehyde is most important as it is released in dosage forms from plasticizers and preservatives, fats, and polyethylenated... 

Only compounds in a narrow chromatographic window are normally monitored low molecular weight aldehydes, which may play a significant role in SBS, are not routinely monitored as part of TVOC [119]. 

Celgene developed transaminase technology for the enantioselective conversion of chiral amines to ketones [25]. Low molecular weight aldehydes, such as propional dehyde, were used as the amine group acceptor. This process has been used on a... 

Base-catalyzed self-addition of aldehydes to form -hydroxy aldehydes is successful under mild conditions, but only with relatively low molecular weight aldehydes examples are presented in equations (7) and (8). The rule of thumb is that aldehydes of up to alraut six carbons can be dimerized in aqueous and alcoholic medium by such methods. Attempts to force the addition reaction of higher molecular weight aldehydes by using more vigorous conditions result in dehydration of the initial aldols, with for-... 

Low molecular weight aldehydes. The likelihood of carcinogenicity increases if (i) the compound contains two terminal aldehyde groups separated by less than four interconnecting atoms, and/or (ii) presence of o(,6-double bond. 

Martin, R. S., Villanueva, I., Zhang, J., and Popp, C. J., Nonmethane hydrocarbon, monocarboxylic acid, and low molecular weight aldehyde and ketone emissions from vegetation in central New Mexico, Environ. Sci. TechnoL, 33, 2186-2192, 1999. 

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