Secondary sulfur bonds

Secondary alkanesulfonates are easily biodegradable under aerobic conditions but are less so in an anaerobic environment, a feature common to all sulfonates with the stable carbon-sulfur bond. The recent discussions on anaerobic biodegradation [103] should be put into perspective since in the sewage or deposition path a temporary anaerobic step quickly gives way to a stage where natural conditions, which are aerobic, prevail. Thus, anaerobic biodegradation... 

Carbon-Oxygen and Carbon-Sulfur Bonds. A report of modest enantioselectivity up to 48% ee in the 0-alkylation of racemic secondary alcohols (a kinetic resolution) in the presence of a chiral non-racemic non-functionalized quat, (S)-Et3NCH2CH(Me)Et Br, could not be repeated [80]. Such catalysts would not be capable of making the multipoint interaction between catalyst and reactants in the transition state, which are thought to govern the stereochemistry of these types of reactions. Other O-alkylations are noted [lie]. 

The secondary stmctures of proteins do not describe completely the arrangement of these macromolecules. There may, for instance, be sections that may exhibit some irregularity. Or, some sections may be linked chemically by sulfur-sulfur bonds of cystine groups. There may also be areas... 

An example of intermolecular secondary bonds for the same tellurium-sulfur pair, leading to a regular supramolecular self-assembly, 29, is provided by phenyltellurium(II) diphenyldithiophosphinate, PhTe-S(S)PPh2, in which intermolecular, secondary Te- -S bonds (3.383 A) are observed the intramolecular primary Te-S bonds are shorter (2.406 A) [59, 60] and fall within the range of single, covalent tellurium-sulfur bonds [61],... 

This type of association is better demonstrated in organobismuth chemistry. Thus, the molecules of diphenylbismuth(III) isopropylxanthate, Ph2BiS2COPr, are self-organized in helical chains, 198, with distinct primary (Bi-S 2.66 A) and secondary (intermolecular Bi- -S 3.23 A) bismuth-sulfur bonds [467]. 

In solution or at the end of emulsion polymerization, tetraalkyl thiuram disulfides are added to the emulsion. Very little reaction occurs at this point. Alkali metal salts of dithiocarbamates, secondary amines, or alkali salts of mercaptoben-zothiazole (28) are added to initiate the peptization reaction through sulfur-sulfur bond cleavage. The polychloroprene sulfide ion reacts with the tetraalkyl thiuram disulfide to cap the end of the polymer and generate a second dithiocarbamate salt. The second dithiocarbamate salt propagates the peptization reaction. Thus, the final polymer molecular weight and bulk Mooney viscosity will depend on initial sulfur concentration in the copolymerization and the concentration of tetraalkyl thiuram disulfide and dithiocarbamate salt added during the peptization step. 

An ordered list of the amino acids from the N-terminus (where an amino group remains) to the carboxylic acid terminus (where a carboxylate remains) that also includes bridges across the structure created by sulfur-sulfur bonds from cysteine to cysteine is called the primary structure. The secondary structure of a peptide usually refers to repeating units that give rise to coils or ribbons or other repeating structural variants, while the tertiary structure consists of all of the contributions to the three-dimensional representation. When two or more polypeptide subunits are present in the protein, their relationship is called a quaternary structure. 

From the specific spectra of secondary ions (Fig. 14.2) and comparison between normalized counts for particular cases (Fig. 14.3) it follows, that the highest amount of sulfur, in a form of SH- ions, was transferred to the surface layer of iron counterface by ebonite. In the case of polysulphone, due to strong sulfur bonding to macromolecular backbone (Fig. 14.4) and different from other polymers studied mechanisms of mechano-degrada-tion, the expected effect of sulfur transfer is practically absent. 

Intramolecular Reactions. Tris(trimethylsilyl)silane is an effective mediator of radical cyclizations. In addition to halides and selenides, secondary isocyanides can be used as precursors for intramolecular C-C bond formation, which is impossible using the tin hydride (eq 11). Selective cleavage of the carbon-sulfur bond of a 1,3-dithiolane, 1,3-dithiane, 1,3-oxathiolane, or 1,3-thiazohdine derivative is an efficient process to generate carbon-centered radicals, which can undergo cyclization (eq 12). 

By taking into account the secondary interactions, for structural types (S and T) and (V and W) the coordination geometry at the metal center is pseudo-octahedral, and in (U) and (X), square-based pyramidal. The intramolecular copper-sulfur bonds of 2.2 A are some 0.1 A shorter than those in [Cu(S2CNR2)2], although the intermolecular copper-sulfur interactions are considerably longer (3.1-3.7 A as compared with 2.7-2.9 A). 

Esters. Most acryhc acid is used in the form of its methyl, ethyl, and butyl esters. Specialty monomeric esters with a hydroxyl, amino, or other functional group are used to provide adhesion, latent cross-linking capabihty, or different solubihty characteristics. The principal routes to esters are direct esterification with alcohols in the presence of a strong acid catalyst such as sulfuric acid, a soluble sulfonic acid, or sulfonic acid resins addition to alkylene oxides to give hydroxyalkyl acryhc esters and addition to the double bond of olefins in the presence of strong acid catalyst (19,20) to give ethyl or secondary alkyl acrylates. 

Carbonylation, or the Koch reaction, can be represented by the same equation as for hydrocarboxylation. The catalyst is H2SO4. A mixture of C-19 dicarboxyhc acids results due to extensive isomerization of the double bond. Methyl-branched isomers are formed by rearrangement of the intermediate carbonium ions. Reaction of oleic acid with carbon monoxide at 4.6 MPa (45 atm) using 97% sulfuric acid gives an 83% yield of the C-19 dicarboxyhc acid (82). Further optimization of the reaction has been reported along with physical data of the various C-19 dibasic acids produced. The mixture of C-19 acids was found to contain approximately 25% secondary carboxyl and 75% tertiary carboxyl groups. As expected, the tertiary carboxyl was found to be very difficult to esterify (80,83). 

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