Covalent alkylation

These observations do not, however, mean that TBT carboxylates and TBTCl are ionic in nature. After detailed analysis of the physical evidence such as the low specific conductance and dipole moment of trialkyltin halides, Neumann has concluded that they have no "salt-like constitution" (6). Bonding in the trialkyltin carboxylates also is essentially similar to that in covalent alkyl esters, as evidenced by the low dipole moment of 2.2D for tributyltin acetate in benzene, as compared to 1.9D for alkyl acetates (7). 

An alkyl such as KCH3 - which is considered to have much ionic character - might therefore be expected to decompose on contact with water, just as ionic hydrides do. More covalent alkyls/aryls are susceptible to hydrolysis according to the scheme ... 

The existence and preparation of stable dinitramides was disclosed publicly in two patent applications filed by the US military contractor SRI [1,2]. They cover a series of dinitramide salts, including ADN. The anion, N(N02)2", was named here for the first time as dinitramide, in contrast to the covalent alkyl compounds called dinitramines. The protonated form of the dinitramide anion was named dinitraminic acid, HN(N02)2. 

It should be stressed that growing species with diffused charge distributed along —N—C—0— group are relatively weak electrophiles. Thus, as discussed in Section II.B.6.C, ionic active species may exist when coupled with relatively nucleophilic counterions such as Br or I". The collapse of ion pairs into covalent alkyl halide end groups does proceed in the system, but these covalent species still react (although slower than... 

Polymerization was initiated with alkylating agents such as CH3I, CeHsC Br, or CH3OSO2CF3. Depending on the nucleophilicity of the counterion, propagation proceeds on phosphonium ion active species (triflate counterion) or on covalent alkyl bromide species. 

Formation of ionic species from covalent alkyl tosylate and monomer will be favored in the initiation reaction by a polar medium which can solvate and stabilize the resulting ion pair. In these polymerizations, the Initial medium was 80% o-dlchlorobenzene with the rest monomer and initiator, which was of low polarity (e(O-DCB)= 9.8, e(2-isobutyl oxazollne) 4). The relatively nonpolar medium slows down the initiation considerably. The propagation reaction requires the coordination of the monomer to the oxazollnium ion. The propagation is faster when the solvent is non-nucleophllic (15). 

The rare-determining steps" of Tjoth Initiation and propagation are the dipole-dipole Sjj2 reactions between and alkyl iodide and monomer producing transient phosphonlum species such as 18 and 21, which are converted rapidly into covalent alkyl iodide species ... 

Fosfomycin is one of a few natural products containing a carbon-phosphorus (C— P) bond isolated from Streptomyces fradiae, Streptomyces viridochromogenes, and Streptomyces wedmorensis [73]. It was also isolated from Pseudomonas syringae and Pseudomonas viridiflava [74, 75], Fosfomycin is a highly effective antibiotic of low toxicity clinically utilized for the treatment of lower urinary tract infections [76] as well as methicillin-resistant [77] and vancomycin-resistant [78] strains of S. aureus. Moreover, fosfomycin is effective for the treatment of cephalosporin- and penicillin-resistant Streptococcus pneumonia [79] and ciprofloxacin-resistant E. coli [80], The antimicrobial activity of fosfomycin has been ascribed to the inactivation of UDP-GlcAAc-3-O-enolpyruvyltransferase (MurA), an essential enzyme that catalyzes the first committed step in the biosynthesis of peptidoglycan, the main component of the cell wall, by covalent alkylation of an active site cysteine [81]. 

Polymer/surfactant complexes may exhibit thermotropic mesomorphism as well as the lyotropic one discussed above. Among conducting polymers, PANi has been of considerable scientific interest because of its unique electrical and optical properties and environmental stability. Besides the covalent alkyl substitution di.scussed above, a significant approach has been to use functionalized acids, which usually serve as surfactants. Dodedcylbenzenesulfonic acid (DBSA) has been widely used for protonation of PANi and found to improve the solubility and processibility of the conducting polymer. 

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