Andrea Boaretto

Ion Chromatographic Determination of Nitrite in the Presence of a Large Amount of Chloride.

Abstract Different procedures for the quantitation of nitrite in the presence of a large excess of chloride are described. The results obtained show that, in general, solutions characterized by N0 2 - /Cl - ratios of about 1/10 000 can very easily be analyzed. The best results were obtained with amperometric detection in conjunction with NaCI as the eluent which allows ratios down to about 1/700 000 to be employed. One of the procedures investigated was successfully applied to the analysis of samples of sea-water from fish breeding pools.

Allylstannation: VI. Allylation and allenylation of aldehydes and ketones by allyl- and allenyl-tin chlorides in the presence of water

Abstract Allyl- and propargyl-carbinols can be readily prepared in one pot reaction, in the presence of water, by addition of allyl- or allenyl-tin chlorides to carbonyl compounds. The reactions of Bu3-n(CH2CHCH2)SnCln, Bu3-n(CH3CHCHCH2)SnCln (n = 1, 2) and Bu2(CH2CCH)SnCl and the carbonyl compounds RCHO (R = H, C2H5, (CH3)2CH, (CH3)3C, (E)-CH3CHCH, C6H5) and RCOR′ (R = R′ = CH3 and R = CH3 and R′ = (CH3)2CH) have been examined. The monochloroorganotin derivatives undergo the following quantitatvive reactions: Bu2(CH2CHCH2)SnCl + RCOR′ + 1 2 H2O → R(HO)C(R′)CH2CHCH2 + 1 2 [Bu2SnCl]2O↓ (1) Bu2(CH2CHCH2)SnCl + RCOR′ + 1 2 H2O → R(HO)C(R′)CH2CHCH + 1 2 [Bu2SnCl]2O↓ (2) Reaction (2), which involves the allenic substrate, is characterized by rearrangement of the unsaturated chain, the propargylic carbinol being isolated as the major product (∼ 90%).

Allylstannation V. cis-stereoconvergent sysnthesis of homoallylic alcohols and 4-chloro-2,6-dialkyl-3-methyltetrahydro-pyrans by the addition reaction of 1-buten-3-yldichloro-n-butyltin and aldehydes

Abstract 1-Buten-3-yl-n-butyldichlorotin, generated in situ by redistribution of ( E / Z )-2-butenyltri-n-butyltin and BuSnCl 3 , reacts readily with neat RCHO (R = CH 3 , C 2 H 5 , (CH 3 ) 2 CH) at 25°C to give linear alcohols RCH(OH)CH 2 CHCHCH 3 and/or 2,3,4,6-tetrasubstituted tetrahydropyrans, CH 2 CH(R)OCH(R)CH(CH 3 )CH-(Cl), which are mainly in the cis -configuration with respect to the CH(CH 3 )-CH(Cl) bond. When R = (CH 3 ) 3 C and C 6 H 5 , only the homoallylic alcohols are obtained. These cis -stereoconvergent syntheses are explained in terms of kinetic control of the formation of adducts obtained by insertion of one or two aldehyde molecules into the organotin substrate.

Allylstannation: IX. The preparation of 4-chloro-2,6-dialkyl-, 4-bromo-2,6-dialkyl-, (E/Z)-4-chloro-2,6-dialkyl-3-methyl-and (E/Z)-4-bromo-2,6-dialkyl-3-methyl-tetrahydropyrans by condensation of aldehydes with di- and tri-halides of allyltin

Abstract The reaction recently discovered leading to tetrahydropyrans (THP): has been more extensively investigated by using various allyltin systems, alternate incremental additions of two aldehydes, and scrambling organotin reagents. Unsymmetric halotetrahydropyrans containing various R groups can be readily prepared in this way. The thermal breakdown of the 1 2 -dichloro adducts, namely ( E/Z )1-alkyl-1-butyldichlorostannoxy, 1-alkyl-3-pentyl ethers and the ( threo/erythro )-1-alkyl-1-butyldichlorostannoxy, 1-alkyl-2-methyl-3-butenyl ethers, is a stereospecific reaction which affords ( E/Z )-halotetrahydropyrans, where the isomerism is at the CHClCH(CH 3 ) bond.

Preparation of α-allenic and β-acetylenic alcohols by treatment of a mixture of Bu,SnCHCCH;; and RCHO with Bu2SnCl2 and water

Treatment of a mixture of Bu3SnCHCCH2 and RCHO (R = CH3, C2H5, (CH3)2CH, (CH3)3C) with Bu2SnCl2 in the presence of water gives isomeric mixtures of α-allenic and β-acetylenic alcohols with the α-allenic isomer predominating ( ∼ 75%). Reactions carried out without water give mixtures in which the isomeric ratio between the allenic and acetylenic alcohol varies between 7030 and 5050. In contrast β-acetylenic alcohols predominate when HCHO and α,β-unsaturated aldehydes (R = CH2CH, CH2C(CH3), CH3CHCH, C3H7CHCH) are used. The stereochemical course of the reactions appear to depend upon the addition and isomerization rates of the Bu2Sn(CH2CCH)Cl intermediate.

Allylstannation III. Synthesis of homoallylic alcohols and 4-chloro-2,6-dialkyl-3-methyltetrahydropyrans by reactions between (E/Z)-2-butenyldichloro-n-butyltin and aldehydes☆

Abstract 2-Butenyldichloro-n-butyltin (in various cis / trans isomer ratios) reacts readily with neat RCHO (R = CH 3 , C 2 H 5 , (CH 3 ) 2 CH, and C 6 H 5 ) at 25°C to give (a) linear alcohols, RCH(OH)CH 2 CHCHCH 3 in the E and Z forms, (b) branched alcohols, RCH(OH)CH(CH 3 )CHCH 2 in the threo and erythro forms, and (c) 2,3,4,6-tetra-substituted tetrahydropyrans (A) as a mixture of cis / trans isomers arising from the CH(CH 3 )CHCl bond. The maximum yields of these tetrahydropyrans were obtained by the use of 3–3.5 molar ratios RCHO/tin compound in the absence of solvent, whereas work-up after reactions in CH 2 Cl 2 gave linear, alcohols as the main products. The formation of linear alcohols appears to be stereospecific, as the ratio of E / Z isomers obtained is the same as that in the organotin compound. Tetrahydropyrans are formed preferentially as the trans isomers.

Allylstannation: VII. Preparation of carboxylic acid 1-alkene-4-yl and 1-alkyne-4-yl esters by transalkoxylation of 4-n-dibutylchlorostannoxy-1-alkenes and 4-n-dibutylchlorostannoxy-1-alkynes with acyl chlorides

Abstract Carboxylic acid 1-alkene-4-yl and 1-alkyne-4-yl, esters (RCH(CH 2 CHCH 2 )OCOR′ ad RCH(CH 2 CCH)OCOR′, R = R′ or R ≠ R′ = alkyl or alkenyl group) can be readily prepared in high yields by transalkoxylation reactions between 4-n-dibutylchlorostannoxy-1-alkenes or 4-n-dibutylchlorostannoxy-1-alkynes with acyl chlorides. This represents a general route for preparation of esters containing allyl or propargyl groups.

Ion chromatographic determination of N-nitrosoglyphosate in a glyphosate matrix

Abstract The use of high-performance ion chromatography (HPIC) for the determination of N -nitrosoglyphosate [ N -nitroso- N -(phosphonomethyl)glycine] is reported. NMR, spectrophotometric and electroanalytical measurements showed that two conformers of N -nitrosoglyphosate in slow equilibrium are always present. Separation of these conformers is achieved by using appropriate chromatographic conditions. The conductimetric detection of N -nitrosoglyphosate and glyphosate and application to the determination of traces of N -nitrosoglyphosate in complex matrices are also reported.

UV spectrophotometric detection in the ion chromatographic analysis of alkali and alkaline earth metal and ammonium cations

Abstract A spectrophotometric detection procedure for the high-performance ion chromatographic determination of alkali and alkaline earth metal and ammonium cations, after chemical suppression of the eluent, is proposed. Measurements at 200 nm revealed the presence of hydroxide ions, which bear a stoichiometric relationship with the eluted M + cations. The detection limits and sensitivities were similar to those obtained by the usual conductivity method. The suggested procedure, when tested in the analysis of samples of ammonium cations, gave responses dependent also on the pH of the suppressed solution and relative p K a values. Fitting of the calibration graphs by means of a non-linear regression routine also allows the determination of the equilibrium constants of the cations.