Intersequence cyclization in copolymers of N-vinyl carbamates

Monomer reactivity ratios determined for the copolymerization of tert-butyl N-vinylcarbamate (r_A = 0.55 ± 0.05) with phenyl N-vinylcarbamate (r_B = 2.08 ± 0.15) indicate that the monomer units are distributed randomly along the polymer chains. The following sequence of reactions was used to cause intersequence cyclization between tert-butyl N-vinylcarbamate and phenyl N-vinylcarbamate units in the copolymers. The extent of cyclization obtained was in accord with that expected for random copolymers.      

Regioselective hydroborations of methylvinylchlorosilanes

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl_nMe_3?nSiCHCH₂ (n= 0 ? 3), has been investigated using BH₃←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols forn= 0 and 1. Forn= 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol-0-d provides a more effective means of derivatization. Addition of the alkenes,n= 2 or 3, to excess BH₃←THF givesca. 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes giveca. 80% of the β-boron adducts.     

Measurement of the Compton profiles of CH4 and C2H4 by high energy electron impact spectroscopy

We present a new experimental determination of the Compton profiles of CH₄ and C₂H₄ molecules using high energy electron impact. The observable q range has been extended up to 10 au (6 au for C₂H₄). Good agreement is found with an earlier X-ray scattering experiment and with new theoretical calculations.     

Reaktionen mit Blei(IV)-acetat,XVI. Eine neuartige Umwandlung von 2-Acetoxy-3-oxo-4,5-epoxy-steroiden

Treatment of 3-oxo-4, 5-oxido steroids with lead tetraacetate results in acetoxylation in the 2α-position as could be shown by independent synthesis of the acetoxylated compounds. The products of this reaction rearrange even under very mild conditions (chromatography on silicagel or alumina) to the corresponding 2,3-dioxo-Δ⁴ compounds. The influence of structure and conformation of the various intermediates on their NMR.-spectra is discussed. A mechanism for this new transformation is proposed.     

Spektralphotometrische Bestimmung des Thioharnstoffs im Mikrogrammbereich

Zusammenfassung Eine spektralphotometrische Methode zur Bestimmung von Mikrogrammengen Thioharnstoff in Gegenwart von Biuret, Cyanat, Cyanursäure, Dicyandiamid, Harnstoff, Melamin und Rhodanid wird beschrieben. Sie beruht auf der Umsetzung des Thioharnstoffs mit salpetriger Säure zu Rhodanwasserstoffsäure, die mit Brom in Bromcyan übergeführt wird. Letzteres wird mit Pyridin und Barbitursäure zu einem intensiv gefärbten, stabilen Polymethinfarbstoff umgesetzt. Störungen durch andere Cyanamidderivate und -folgeprodukte werden untersucht.

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Summary A spectrophotometric method is described for the determination of micro amounts of thiourea in presence of biuret, cyanates, cyanuric acid, dicyanodiamide, urea, melamine and thiocyanates. The method bases on the reaction of thiourea with nitrous acid to thiocyanic acid, which is converted with bromine to cyanogen bromide. The latter forms with pyridine and barbituric acid an intensively coloured, stable polymethine dye. The interferences by other cyanamide derivatives and resultant products have been investigated.

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3. Mitteilune über die Analyse der Cyanamidderivate. 2. Mitteilung siehe ¹⁴.

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Frau S. Mohs möchten wir an dieser Stelle für ihre gewissenhafte Mitarbeit unseren Dank aussprechen.     

Determination of hexamethylene-based isocyanates in spray-painting operations. Part 1. Evaluation of a polyurethane foam sponge sampler

A polyurethane foam (PUF) sponge was mounted in a cassette sampler and evaluated as a sorbent for the collection of hexamethylene diisocyanate (HDI) monomer and HDI-based oligomers. Recovery studies indicated 112 +/- 34% average recovery of HDI monomer and 92 +/- 9% and 97 +/- 25% average recovery of HDI-based oligomers when using impregnated PUF sponges. The PUF sponge was also evaluated during actual spray-painting operations. In a series of side-by-side sampling events, an impinger filled with 1-(2-methoxyphenyl)piperazine (MOP) in toluene was compared directly with a cassette sampler containing a PUF sponge impregnated with MOP or 1-(9-anthracenylmethyl)piperazine (MAP) in dimethyl sulfoxide (DMSO). For the analysis of HDI-based oligomer, there is no significant difference (p < 0.05, n = 7) in the air concentration when sampling with either the PUF sponge cassette or the impinger. The results are significant because they indicate that a PUF sponge, which is more convenient than an impinger, may be used for the collection of HDI-based oligomer generated during spray-painting operations.     

Vacuum balance and related studies of green and red rusts

Green and red rusts are formed when iron is partially or completely oxidised. Analogues of the rusts may be precipitated from iron(II) and iron (III) salt solutions treated with alkali under reducing or oxidising conditions. Variations in surface area and porosity have been investigated by gravimetric nitrogen gas sorption, using vacuum microbalance techniques.Freshly-precipitated red rusts, hydrous iron (III) oxide, have surface areas of about 200–400 m²g^?1. When they are added to iron (II) hydroxide suspensions kept at pH 7, the green Fe (II)-Fe (III) rusts formed have lower surface areas of about 40–100 m²g^?1, depending on the initial iron(II) sulphate concentrations.     

Synthesis of some pyrrolobenzothiazepines via N-aryl-2-thiocyanatopyrroles

Pyrrolo[1,2-a[3,1]benzothiazepines were successfully synthesized from alkylthiopyrroles. The latter compounds were prepared from the appropriate N-aryl-2-thiocyanopyrroles. 2,3-Dihydro-3-oxo-4-phenylthieno[3,2-b]pyrrole ( 29 ) was obtained from acid treatment of the 2-pyrrolylthioacetic acid 28 .     

Encapsulation of pesticides in a starch-calcium adduct

A simple method of encapsulating water-insoluble pesticides in a starch matrix is described. The method consists of mixing the pesticide with alkali starch followed by precipitation with a calcium chloride solution. A starch–calcium adduct that entraps the pesticide in small cells within granular particles is formed. Liquid and solid pesticides were successfully encapsulated by the new method. By use of the herbicide trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine] as core material more than 90% recovery and encapsulation was achieved. Use of acid-modified starches and flours resulted in a lower percentage of encapsulation. Effective encapsulation was also achieved by replacing calcium chloride with strontium chloride or barium chloride.