Labile hydrogen atom

Many inorganic and organic compounds possessing labile hydrogen atoms add acrylonitrile readily with the formation of compounds containing a cyancethyl grouping (—CH j. CH2. CN). This reaction is usually known as cyanoelhylation ... 

The cyclic carbonate of benzoin (4,5-diphenyl-l,3-dioxol-2-one, prepared from benzoin and phosgene) blocks both hydrogen atoms of primary amines after dehydration acid stable, easily crystallizable Sheehan oxazolinones are formed, which are also called Ox derivatives. The amine is quantitatively deblocked by catalytic hydrogenation in the presence of 1 equiv. of aqueous acid (J.C Sheehan, 1972, 1973 M.J. Miller, 1983). An intelligent application to syntheses of acid labile -lactams is given in the previous section (p. 161). 

Adducts of BF and some organic compounds having labile hydrogen atoms in the vicinity of the atom bonding to the boron atom of BF may form a derivative of BF by splitting out HF. For example, P-diketones such as acetylacetone or benzoylacetone react with BF in benzene (38) ... 

Nucleophilic Addition. Reagents with labile hydrogen atoms, such as alcohols, thiols, phenols, carboxyHc acids and amines, add to ketenes giving the corresponding carboxyHc acid derivatives (1) as shown ia Figure 1 (38). Not many are of practical importance, as there are better ways to such... 

Uses. The lowest member of this class, ketene itself, is a powerful acetylating agent, reacting with compounds containing a labile hydrogen atom to give acetyl derivatives. This reaction is used only when the standard acetylation methods with acetic anhydride or acetyl chloride [75-36-5] do not work weU. Most of the ketene produced worldwide is used in the production of acetic anhydride. Acetic anhydride is prepared from the reaction of ketene and acetic acid. 

Ketones with labile hydrogen atoms undergo enol acetylation on reaction with ketene. Strong acid catalysis is required. If acetone is used, isoptopenyl acetate [108-22-5] (10) is formed (82—85). Isopropenyl acetate is the starting material for the production of 2,4-pentanedione (acetylacetone) [123-54-6] (11). 

Liquid ethylene oxide under adiabatic conditions requires about 200°C before a self-heating rate of 0.02°C/min is observed (190,191). However, in the presence of contaminants such as acids and bases, or reactants possessing a labile hydrogen atom, the self-heating temperature can be much lower (190). In large containers, mnaway reaction can occur from ambient temperature, and destmctive explosions may occur (268,269). 

N. A. Tananaev, simultaneously with F. Feigl, developed the spot analysis. Known Tserevitinov method for determining labile hydrogen atoms in organic compounds (1902-1907 should be noted (the method was later improved by A.P Terent ev). In the USSR, there were powerful schools in liquid-liquid extraction and inverse voltammetry. 

For exchange of non-labile organic hydrogen atoms, acid-base catalysis (or some other catalytic hydrogen-transfer agent such as palladium or platinum) is required. The method routinely gives tritiated products having a specific activity almost 1000 times that obtained by the Wilzbach method shorter times are required (2-12h) and subsequent purification is easier. 

No direct nucleophilic substitution of the hydrogen atoms in the isoxazole nucleus a or y to the nitrogen is as yet known. Thus, the Chichibabin reaction fails in the isoxazole series because of the cleavage of the heterocyclic nucleus under these conditions. It is the lability of the isoxazole ring toward nucleophilic reagents that makes the chemical behavior of isoxazole fundamentally different from that of pyridine. 

All the aldehydes hitherto studied, which contain next to the functional aldehydic group one or more labile hydrogen atoms are cap-... 

For polymer containing labile hydrogen atoms, chain peroxidation can lead to hydroperoxide formation. The following reactions are expected to take place. 

Efforts to achieve a retardation of cross-linking in elastomers are based on the general assumption of a radical mechanism for retardation cross-linking and the possibility of its inhibition by a deactivation of the reactive macromolecular radical [33]. These compounds generally contain one or more labile hydrogen atoms, which after, donation of this atom, will form relatively inactive radicals. Typical antirad agents are quinones, hydroquinones, and aromatic amines (phenyl and napthylamines). 

Spectral Transparence Starting from 230 nm -oc 4-Isopropylphenoxy Photooxidable Groups Presence of Labile Tertiary Hydrogen Atoms Photooxydation and Photoreticulation Processes Surface Film Modification ... 

Parker37 defined class 4 as solvents "which cannot donate suitable labile hydrogen atoms to form strong hydrogen bonds with an appropriate species and proposed the designation dipolar aprotic solvents he extended their range down to s > 15 and quoted as examples acetone, acetonitrile, benzonitrile, dimethylformamide, dimethyl sulphoxide, nitrobenzene, nitromethane (41.8) and sulfolane (tetramethylene sulphone) (44), where e varies from 21 to 46.5, and the dipole moment p from 2.7 to 4.7 debye. 

The most versatile approach to disulfonium dications - reaction of triflic anhydride with monosulfoxides of bis-sulfides - has certain limitations in the case of selenium. Most importantly, selenoxides that contain (3-hydrogen atoms are labile.120 122 Trimethylsilyl triflate was used instead of triflic anhydride for synthesis of dication 112 from a selenoxide 111 (Scheme 43).123... 

Each alternate carbon in the Polymer chain of polypropylene has been a tertiary hydrogen atom which is relatively labile. Thus compared to polyethylene it becomes more prone to attack by oxidising agents. 

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