Sulfur-containing carboxylic acids

The data in Figures 33 and 34 show typical thermodynamic properties (normal Marcus region) for the electron transfer reaction. In these examples, the rate of the process increases as the driving force of the reation (—AGet) increases. The properties observed in Figures 33 and 34 also predict the type of radical formed after electron transfer. From studies of sulfur-containing amino acids and sulfur-containing carboxylic acids [170-175] it is known that decarboxylation occurs only if the carbox-... 

Sulfur-containing amino acids (SC A A) and sulfur-containing carboxylic acids (SCCA )... 

A series of sulfur-containing carboxylic acids demonstrate similar photophysical and photochemical features as electron donors. This is demonstrated in Table 11 [ 184]. 

Table 11. Photophysical and photochemical properties of sulfur-containing carboxylic acids tested as electron donors is 4-carboxybenzophenone-sensitized polymerization.

In this section an illustrative discussion on kinetics of photopolymerization initiated via an intermolecular photoinduced electron transfer for a dye-tertiary aromatic amine initiating photo-redox couple [193] and for 4-carboxybenzophenone-sulfur-containing carboxylic acids initiating systems will be presented. 

Kinetic analysis gives additional information related to the reactivity of the free radicals obtained during the processes following a photoinduced electron transfer process. A variation in radical reactivity could be caused, for example, by their stability or their reactivity with monomer, as in the case of photoinitiation by 4-carboxybenzophenone-sulfur-containing carboxylic acid of free-radical polymerization [184]. 

Figure41. Relationship between the rate of polymerization of acrylamide and quantum yield of free radicals formation for 4-carboxybenrophenone (CB)-sulfur-containing carboxylic acids (SCCA) initiating system. SCCA listed in Table 11.

The Dim ester was developed for the protection of the carboxyl function during peptide synthesis. It is prepared by transesterification of amino acid methyl esters with 2-(hydroxymethyl)-l,3-dithiane and Al(/-PrO)3 (reflux, 4 h, 75°, 12 torr, 75% yield). It is removed by oxidation [H2O2, (NH4)2Mo04 pH 8, H2O, 60 min, 83% yield]. Since it must be removed by oxidation it is not compatible with.sulfur-containing amino acids such as cysteine and methionine. Its suitability for other, easily oxidized amino acids (e.g., tyrosine and tryptophan) must also be questioned. It is stable to CF3CO2H and HCl/ether. - ... 

Surfactants are prepared which contain carboxylic acid ester or amide chains and terminal acid groups selected from phosphoric acid, carboxymethyl, sulfuric acid, sulfonic acid, and phosphonic acid. These surfactants can be obtained by reaction of phosphoric acid or phosphorus pentoxide with polyhydroxystearic acid or polycaprolactone at 180-190°C under an inert gas. They are useful as polymerization catalysts and as dispersing agents for fuel, diesel, and paraffin oils [69]. 

When simulating the interaction of amino acids with a silica surface in a biological medium, the zwitterionic form as well as hydration should also be taken into consideration.12 Shielding of functional groups (amino, carboxyl, and thiol) of sulfur-containing amino acid molecules by water molecules results in... 

In the present paper new results are reported on the radiation-induced formation of sulfur-containing amino acids. Aqueous ethylamine served as a model substrate. It was carboxylated in the presence of sodium sulfide or hydrogen sulfide leading to the formation of cystine, cysteine, cysteic acid and other amino acids. 

Amino acids can be classified according to their substituent R groups (Fig. 1.2 to Fig. 1.8) in basic amino acids, R contains a further amino group, whereas in acidic amino acids, R contains a further carboxyl group. In addition, there are aliphatic, aromatic, hydroxyl containing and sulfur containing amino acids according to the nature of the substituent, as well as a secondary amino acid. 

If there is more than one substituent on the pyridine ring the compound will be found in the table vatii the functional group listed last in the above list. For example, 4-chloro-3-nitro-6-n-propyl-2-pyridinol is listed in the table with the heading Nitro and Nitroso 2-Pyridinols. In all cases except sulfur containing pyridinols and carboxylic acids and their derivatives, the functional group is directly attached to the pyridine ring. In the latter cases the sulfur or carboxylic acid may appear in any location on the substituent. 

Polymers that contain carboxylic acid functionality, such as carboxylated nitrile rubber (XNBR), can also be cross-linked with a divalent metal oxide, either zinc oxide, zinc peroxide, or magnesium oxide. The organo-metallic cross-link supplements the traditional sulfur or peroxide generated cross-links to provide superior toughness and abrasion resistance. In XNBR, the amount of ZnO depends on its surface area, with 5 phr at 9 m /g surface area being used compared with 9 phr at 3.5 m /g surface area. Standard XNBR grades are best cured with zinc peroxide or low... 

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