Precautions autoxidation

Normal precautions for chemicals of mild toxicity are appHcable to the safe handling and storage of commercial tetrahydrofurfuryl alcohol. Discoloration in storage rarely occurs if the proper precautions are observed prevention of exposure to air wiH prevent autoxidation. The Hst price of tetrahydrofurfuryl alcohol (1997) is 1.15/lb. 

Compounds that contain allylic and benzylic centres are especially prone to autoxidation, since the radicals formed on oxidation are stabilised by resonance. Oleic acid contains two allylic positions, linoleic acid contains two allylic positions and one double allylic position, while linolenic contains two allylic and two double allylic positions. We would therefore expect linolenic to be the most susceptible acid to oxidation, followed by linoleic and oleic. (The actual relative rates of autoxidation are linolenic (25) > linoleic (12) > oleic (1)). Precautions that can be employed to minimise oxidative deterioration are reducing the oxygen concentration in the container by, for example, the use of an inert atmosphere, and the use of a well-closed and well-filled container. It would also be advisable to store the product at low temperature and in a dark place. 

The danger associated with organic peroxy compounds makes it essential to maintain the safety precautions described in the Section on Hydroperoxides and peroxides by autoxidation. The behavior of an untested olefin on oxidation must be tested on a small sample before larger amounts are brought into reaction. Reaction mixtures must be worked up only after destruction or extraction of the excess of peroxy acid by alkali hydroxide solutions (danger of explosion ). 

There are overwhelming reports on superoxide anion generation in defined biological systems including redox reactions of small molecules, autoxidable proteins and oxidative enzymes The most prominent enzyme is xanthine oxidase. However, some precautions are neccessary, because the single electron reduction of dioxygen is considered to be an unnatural reactivity of this enzyme, which, under in vivo conditions acts like a dehydrogenase... 

Acetaldehyde should be handled in the laboratory using the "basic prudent practices" described in Chapter 5.C, supplemented by the additional precautions for dealing with extremely flammable substances (Chapter 5.F). In particular, acetaldehyde should be used only in areas free of ignition sources, and quantities greater than 1 hter should be stored in tightly sealed metal containers in areas separate from oxidizers. Acetaldehyde should always be stored under an inert atmosphere of nitrogen or argon to prevent autoxidation. 

Storage at low temperature in the dark. The autoxidation rate is thereby decreased substantially. However, in fruits and vegetables which contain the lipoxygenase enzyme, these precautions are not applicable. Food deterioration is prevented only after in activation of the enzyme by a blanching process (cf. 2.6.4). 

As constant repetition is tedious, it will be assumed in all the subsequent discussion of methodology in this book that precautions will be taken at all times to minimise autoxidation. 

Precautions should be taken at all times to prevent or minimise the effects of autoxidation (see Chapter 2). 

It should be remembered that it is almost always advisable to calculate molar rather than weight proportions (or percentages) of any molecular species isolated. Precautions should be taken to minimise the effects of autoxidation (see Chapter 2). Procedures for the analysis of molecular species of lipids have been dealt with in several monographs [163,168,506,510] in addition to many shorter reviews on specific topics (see below). 

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