Adriana E. Zúñiga

Transmetallations between aryltrialkyltins and borane: synthesis of arylboronic acids and organotin hydrides

Abstract Aryltrialkyltin compounds react with borane in THF to give mixtures of trialkyltin hydrides and arylboranes, which on hydrolysis give arylboronic acid in high yields. The arylboronic acids are easily separated and obtained free of organotins.

Chemo- and stereoselective reduction of (pivaloyloxy)methyl 6,6-dihalopenicillanates by trineophyltin hydride: Selective synthesis of 6β-halopenicillanates

Abstract A new Triorganotin hydride, Trineophyltin hydride was prepared and its chemo- and stereoselectivity towards reduction of Pom 6,6-homo- and hetero- dihalopenicillanates was examined. The trineophyltin hydride reveals higher stereoselectivity compared to that by tributyltin hydride at 25°C.

Preparation and some reactions of neophyltin anions

Abstract A study on the preparation of trineophyltin and mixed methylneophyltin anions and subsequent reactions of these anions is reported. It was found that whereas mixed hydrides Me n Nph 3− n SnH ( n = 1,2) react with NaH in DMSO to give the corresponding organotin sodium anions (60–70% yield), trineophyltin hydride reacts with NaH to give hexaneophylditin as the only product (32%). The reaction of tin halides Me n Nph 3− n X (X = Cl, Br; n = 0, 1, 2) with lithium in THF yields the corresponding organotinlithium anions (70%). The tin anions were reacted with various alkyl halides. The 1,4 addition of trineophyltinlithium ( 10 ∗ ) to α,β-unsaturated enones followed by the reaction of the intermediate carbanions with methyl iodide, leads with benzylideneacetone to a mixture of the corresponding threo (34%) and erythro (25%) diastereoisomers. Under the same reaction conditions, the addition of 10 ∗ to chalcone proceeded with complete stereoselectivity to give the diastereoisomer threo (60%) as the only product. Full 1 H and 13 C NMR data of the new organotins are given.

Synthesis, characterization and evaluation of reactional parameters on substitution degree of N-hexyl-N-methylene phosphonic chitosan

N-methylene phosphonic chitosan (NMPC) is treated with hexyl aldehyde to give an imine, which is easily converted into N-hexyl-N-methylene phosphonic chitosan (HNMPC) under mild conditions. The structure of this new chitosan derivative is characterized by FT- IR, 1H, 13C, 31P, 1H13C-HSQC NMR, SEM and XRD. The influence of reactional parameters on the substitution degree (DS), evidenced that a mol ratio 1.50:1.00 (hexyl aldehyde: free amino groups); a reaction time of 1 h. and 45 °C of temperature afford the best DS. HNMPC molecular weight is 12,768.62 Da. It shows good emulsifying properties giving o/w emulsions with high stability in time. Microscopic observation as well as particle size distribution show an unimodal droplet size distribution with low droplet diameters. Preliminary tests lead us to believe that this new polymer has good film forming properties.

Physico-chemical studies and emulsifying properties of N-propyl-N-methylene phosphonic chitosan.

Chitosan is a modified, natural carbohydrate polymer derived by deacetylation of chitin. Due to the presence of two functional groups can undergo many chemical modifications. In a previous work we described the synthetic strategy and characterization of a novel soluble derivative: N-propyl-N-methylene phosphonic chitosan (PNMPC). In the study of some physicochemical properties, results showed that this modified chitosan aggregates in several steps when the concentration is increased. By addition of NaOH the initially coiled molecules stretch exposing more phosphonic acid groups to neutralization and finally give a cooperative reaction with OH((). PNMPC has emulsifying properties and gives O/W emulsions with quasi-monodisperse small droplets. Emulsions with 0.18% PNMPC and 30:70 o:w ratio exhibited the best emulsifying properties within the test range. This emulsion ratio showed high stability to long time storage and several successive freeze/thaw and heating/cooling cycles.