Scavenging agents aldehyde scavenger

With aldehydes, primary alcohols readily form acetals, RCH(OR )2. Acetone also forms acetals (often called ketals), (CH2)2C(OR)2, in an exothermic reaction, but the equiUbrium concentration is small at ambient temperature. However, the methyl acetal of acetone, 2,2-dimethoxypropane [77-76-9] was once made commercially by reaction with methanol at low temperature for use as a gasoline additive (5). Isopropenyl methyl ether [116-11-OJ, useful as a hydroxyl blocking agent in urethane and epoxy polymer chemistry (6), is obtained in good yield by thermal pyrolysis of 2,2-dimethoxypropane. With other primary, secondary, and tertiary alcohols, the equiUbrium is progressively less favorable to the formation of ketals, in that order. However, acetals of acetone with other primary and secondary alcohols, and of other ketones, can be made from 2,2-dimethoxypropane by transacetalation procedures (7,8). Because they hydroly2e extensively, ketals of primary and especially secondary alcohols are effective water scavengers. 

Scavenging endogenous and exogenous toxic aldehydes and glycating agents... 

One of the most interesting papers on ascorbic acid-Cu reactions showed that ascorbic acid-Cu catalyzes the formation of ethylene from several precursors. The interest in ethylene was as an abscission agent in plants. All alcohols, aldehydes, acids, ethers, and epoxides formed ethylene when mixed with Cu and ascorbic acid in 5-mL closed bottles at 30 °C for 1 h. Methional was the most active, followed by propanal, propanol, propyl ether, ethyl ether, and ethanol. This reaction may be part of the oxygen scavenging system because Cu increases ascorbic acid s ability to scavenge oxygen. The authors claim this reaction cannot be attributed to copper in its lower valence state. 

Besides acting as an electron scavenger, the precise role of O2 has been elusive for some time and continues to be a subject of some debate. In several studies on the photocatalysed oxidation of aliphatic hydrocarbons, alcohols, ketones, carboxylic acids and aldehydes, Heller (1995) concluded that molecular O2, and not the photogenerated hole or OH radical, is the primary oxidising agent. As evidence, data were given that photooxidation of n-octane films on water produced only traces of octanols. 

Mechanism In the formation of the ylide firom CBr4, two equivalents of triphenylphosphine are used. One equivalent forms the ylide while the other acts as reducing agent and bromine scavenger. The addition of the ylide to the aldehyde is comparable to a Wittig reaction and leads to a dibromoalkene. 

A different kind of moisture-activated IK urethane adhesive utilizes a moisture-activated curing agent such as oxazolidine (51). Oxazolidines are formed by dehydration and subsequent ring closure of aminoalcohols by aldehydes or ketones. When the presence of water causes that reaction to reverse, hydroxyl and amine groups are formed. These react readily and directly with isocyanates. Monooxazolidines are useful primarily as water scavengers, but bisoxazolidines can participate in the curing reactions of urethane adhesives. 

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