B.S. Shasha

A facile route to trans cyclic carbonates of sugars

Abstract Five-membered, cyclic carbonates are formed when vicinal trans -hydroxyl groups in D -glucopyranosides are treated with ethyl chloroformate in the presence of triethylamine. With these reagents, methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-carbonate ( 2 ), methyl 2,6-di- O -(methylsulfonyl)-α- D -glucopyranoside 3,4-carbonate ( 5 ), and methyl 4- O -(ethoxycarbonyl)-6- O -( p -tolylsulfonyl)-α- D -glucopyranoside 2,3-carbonate ( 8 ) were prepared. In contrast, when pyridine is the base present, only acyclic carbonates are formed.

Controlled release formulations of atrazine in starch for potential reduction of groundwater pollution.

Abstract The availability of the herbicide atrazine [2-chloro-4-ethylamino-6-isopropylamino- s -triazine to a soil-water system was greatly diminished by entrapping the herbicide in starch granules. Factors influencing the preparation of and release from these granules were determined. The delivery of atrazine from the granules to a soil-water system was compared with delivery to water. Availability of atrazine from unentrapped commercially available atrazine was also determined. In 15 minute soil-water tests, the rate of delivery of atrazine at a constant level of active ingredient increased as the surface area available in the formulations increased, which was made possible by decreasing the loading, by making the granules smaller, and by improving the degree of atrazine dispersion during granule formulation. Aging of the starch formulations from one to nine days diminished atrazine release. When the soil-water tests were conducted over 20 days, the larger granules (14–20 mesh), as a result of the smaller sample size, released atrazine slower than smaller granules (20–40 mesh). The larger granules induced 35% of saturation in 6 days and the smaller induced 45% of saturation in 3 days. Controlled release over these intervals was proportional to the square root of time according to the theory for controlled matrix diffusion. The larger granules kept in water under these conditions showed release to cause over 70% of saturation in 4 days and indicated that over 60% of the available atrazine was adsorbed by the soil. Atrazine present in saturated aqueous solutions was about 80% recoverable under the conditions of filtration and extraction. No controlled release was observed in soil-water mixtures.

The effect of α-amylases upon the release of trifluralin encapsulated in starch

Abstract Release of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] encapsulated in starch was induced by water and starch-degrading α-amylases. Factors investigated that influenced the rate of release are: encapsulation procedure, particle size of the encapsulated material, and pH of the medium. Variations within a procedure such as additional covalent crosslinking, starch retrogradation, and inclusion of enzyme inhibitors can affect the rate of release. For the three basic encapsulation methods used (xanthide, calcium, or borate), the rate of release was borate > calcium > xanthide when the particles were placed in pH 6.0 buffer. Coarse fractions (4–8 mesh) released trifluralin at less than one-fifth the rate of fine fractions (20–40 mesh). Release rates varied little upon varying the source of the α-amylase or the level of active ingredient (4–20%) within the particles. Trifluralin release from particles prepared by the borate procedure was slowed by crosslinking of the starch matrix with epichlorohydrin and by addition of heavy metal ions. The ability to detect variations in the rate of release as a function of these variables can serve as a basis for producing starch-encapsulated herbicides for particular end uses.

Reaction of starch with carbohydrate trans-carbonates☆

Abstract Mono- and poly-saccharides possessing certain substituted, vicinal, trans-hydroxyl groups are readily substituted onto starch. Such substitution occurs when a trans-fused, cyclic carbonate derivative of the saccharide is added to starch in the presence of a basic catalyst. Excellent yields of products result on addition of methyl 4,6-O-benzylidene-α- d -glucopyranoside 2,3-carbonate (or 2,3-thionocarbonate), and methyl 2,6-di-O-(methylsulfonyl)-α- d -??? 3,4-carbonate to starch in the presence of triethylamine. ??? of degree of substitution (DS) 0.40 and dextran carbonate of Ds 0.31 ??? with starch under various conditions, in the presence of different catalysts, to give ??? corresponding polysaccharide copolymers.

Autoencapsulation: A new method for entrapping pesticides within starch

Abstract A simple method to entrap pesticides under mild conditions is described. Pesticide is mixed with pregelatinized starch or ungelatinized starch containing a gelatinizing agent and enough water is added to allow agglomeration into 12- to 40-mesh granules. At this stage, much of the pesticide is not entrapped but is held firmly enough by the granules for handling. When the granules become wet, they also become gelatinous and then on drying form a solid matrix encapsulating the pesticide. Several pesticides were encapsulated by this method, and the encapsulation efficiencies for encapsulated products were determined.

2,3-thionocarbonate and 2,3-carbonate derivatives of D-glucopyranosides

Abstract A unique sugar derivative, methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-thionocarbonate, which contains a trans -fused ring-structure, was prepared in good yield by rearrangement of bis(methyl 4,6- O -benzylidene-2- O -thiocarbonyl-α- D -glucopyranoside) disulfide. The thionocarbonate was converted into the novel methyl 4,6- O -benzylidene-α- D -glucopyranoside 2,3-carbonate in 93% yield by treatment with silver nitrate. By following the same reaction sequence, 2,3-thionocarbonate and 2,3-carbonate groups were introduced into 6- O -tritylamylose. The rearrangement of bis( O -thiocarbonyl) disulfide derivatives provides a new route for the synthesis of carbohydrate thionocarbonates and carbonates previously unavailable.

Ring-opening reactions of trans-carbonates and thionocarbonates

Abstract The reaction of methyl 4,6- O -benzylidene-α-D-glucopyranoside 2,3-carbonate ( 1 ) and the corresponding 2,3-thionocarbonate ( 2 ) with various nucleophines was investigated. Under proper conditions, 1 and 2 reacted with methanol, benzyl alcohol, α-toluenethiol, ammonia, piperidine, and glycine to give the corresponding 2- O -and 3- O -carbonyl and thiocarbonyl adducts, which were obtained in crystalline form. In each reaction product the 2-isomer was preponderant.

BIOACTIVITY OF CONTROLLED RELEASE FORMULATIONS OF STARCH­ ENCAPSULATED EPTC*

Abstract Using a bioassay technique, the biological activities of starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) were determined in relationship to their controlled release characteristics. The bioactivity of the highly volatile herbicide EPTC was retained on a wet soil surface for 6 to 8 days by starch encapsulation utilizing several crosslinking processes (both chemical and non-chemical) and starches with different ratios of amylopectin to amylose. The rate of release, a measure of the integrity of the granule, depended on the nature of the starch and the crosslinking process. With the herbicide EPTC, encapsulation with a pearl or high amylose starch utilizing the jet-cooking process produced the best controlled release formulation even under the most adverse conditions.

O-(alkyl- and aryl-oxythiocarbonyl) sugar derivatives☆

Abstract Bis(1,2:5,6-di- O -isopropylidene-3- O -thiocarbonyl-α- d -glucofuranose) disulfide ( 1 ) in pyridine undergoes a fragmentation reaction when treated with excess methyl, ethyl, propyl, or butyl alcohols, or phenol, to give the corresponding O -oxythiocarbonyl derivatives ( 2 – 6 ). A faster reaction and higher yield result when iodine is included in the pyridine solution. The oxythiocarbonyl compounds are stable when distilled (near 190°) under diminished pressure. Selective, acid hydrolysis of 3- O -(ethoxythiocarbonyl)-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose ( 3 gave 3- O -(ethoxythiocarbonyl)-1,2- O -isopropylidene-α- d -glucofuranose ( 10 ), which rearranged, on standing in triethylamine, to 1,2- O -isopropylidene-α- d -glucofuranose 5,6-thionocarbonate ( 12 ). Oxidation of 3 with lead tetraacetate or silver nitrate gave the corresponding 3- O -ethoxycarbonyl derivative ( 8 ), whereas reduction of 3 with Raney nickel gave 3- O -(ethoxymethylene)-1,2:5,6-di- O -isopropylidene-α- d -glucofuranose ( 11 ).

Entrapment of herbicides in starch for spray applications

Abstract Sprayable controlled-release formulations were made with the herbicides trifluralin, 2,4-D ester, alachlor and butylate. Aqueous dispersions of gelatinized cornstarches or flours containing herbicides were sprayed and dried to water-resistant films that entrapped the herbicide. Formulations containing 3% Miragel®, 3% cooked pearl, or 7% pregelatinized corn flour and one tenth these levels of active ingredient (a.i.) provided as emulsifiable concentrates had stable viscosities in the 75–260 cP range over 24 hours. The best entrapment was obtained by cooking 3% starches or flours at least 30 min at 100° C and dispersing the emulsifiable concentrates into the cooled whole pastes. Dried formulations based upon 3% Miragel® entrapped 88% trifluralin, 96% 2,4-D ester, 75% alachlor, and 9% butylate. Butylate retention increased to 42% with 6% Miragel® that had been pyrolyzed 1 h at 200° C. Release of trifluralin from Miragel® in the presence of αamylase solution increased with decreasing particle size and increasing level of active ingredient.