摘要:

Thermal organosolv glycol lignins and their fractions have been characterized by means of elemental composition, molecular weight distribution, and1H and13C NMR spectroscopy. Fractionation of each lignin by sequential solvent extraction produced fractions of increasing molecular weight and polydispersity. Structures in the highest molecular weight fractions were found to be linked by a high proportion of β-O-4 type bonds, whilst the lowest molecular weight fractions consisted of a high content of saturated aliphatic side-chain structures. A noticeable difference in the content of carbohydrate contaminants in both starting lignins indicated the formation of relatively stable lignin–carbohydrate complexes, especially in the lignin recovered from pretreated wood. In addition, depolymerization of the lignins and their fractions to monomeric compounds was explored using alkaline hydrolytic and nitrobenzene oxidative routes. The highest molecular weight fractions from each lignin were identified as the best candidates for production of useful monomeric phenolic compounds.

ISSN:0008-4042    

DOI:10.1139/v93-103

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Excess molar volumes, excess viscosities, and excess energies of activation for viscous flow have been determined for then-decane + 1-chlorodecane system at different temperatures, over the whole concentration range. The Prigogine–Flory–Patterson model for solution thermodynamics has been used to calculate the excess molar volumes. Grunberg and Nissan, McAllister, Teja and Rice, and Schrodt and Akel models have been used to calculate viscosity coefficients and these were compared with experimental data for the mixtures.

ISSN:0008-4042    

DOI:10.1139/v93-104

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

In the presence of a Lewis acid, 4-hydroxymethylsydnones undergo reaction with alcohols and benzene to form 4-alkoxysydnones1a, bis(4-sydnonylmethyl) ethers1b, or 4-benzylsydnones1ddepending upon the reaction conditions. At 0 °C, compounds1aand1bare formed from compound1in benzene and alkyl alcohol, respectively. Compound1bis converted to compound1dat 40 °C. When the reactions are carried out in a cosolvent of benzene and methyl alcohol at 40 °C, compound1ais obtained preferentially and followed by conversion to compound1d. The α-sydnonyl-methylene cation derived from either compound1or1ais responsible for the formation of compound1d.

ISSN:0008-4042    

DOI:10.1139/v93-105

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Titrimetric and spectrophotometric methods are developed for the estimation of hypophosphite (PO23−) at mmol and micromol ranges, respectively. In these methods thallium(III) is used as an oxidant and the reduced thallium(I) is determined either oxidimetrically by potassium bromate in the titrimetric method or by measurement of the optical density of thallium(III) at 260 nm in the presence of 0.1 M NaCl and 1 M HClO4in the spectrophotometric method. Convenient methods are described for the determination of ternary mixtures of hypophosphite (PO23−), phosphite (PO33−), and oxalate (C2O42−). A method is also described for the estimation of thallium(III) using hypophosphite as reductant, and the method is applied to the determination of mixtures of thallium(I) and thallium(III).

ISSN:0008-4042    

DOI:10.1139/v93-106

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Using the TiCl3–H2O2, –NH2OH, −Na2S2O8, and −H2O2/Na2SO3, continuous-flow, radical-generating methods at 25 °C, we have successfully characterized by electron paramagnetic resonance spectroscopy radicals formed by the reaction of each of the substrates 2- and 3-fluoropropene with the radicals •OH, •NH3+, •OSO3−, and •SO3−, respectively. With 2-and 3-fluoropropene, respectively, the radicals identified were of general formula CH2(X)ĊFCH3and CH2(X)ĊHCH2F where -X is the added group, except that treatment of 3-fluoropropene with the TiCl3–H2O2reaction system also yielded •CH2CH(X)CH2F. The results obtained are discussed in terms of the effect of the presence of the fluorine substituent on both the apparent reactivity of the substrate molecules towards the radical-generating systems and the spectroscopic properties of the radicals observe

ISSN:0008-4042    

DOI:10.1139/v93-107

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Chiral oxime ethers are readily prepared from chiral alkoxyamines derived from ephedrine and norephedrine. These chiral oxime ethers of isobutyraldehyde and benzaldehyde undergo 1,2-nucleophilic addition reactions with alkyllithium reagents (n-BuLi, PhLi andn-BuLi,tert-butyllithium, respectively) to afford the chiral alkoxyamines with a diastereomeric excess of 64–88%. Reduction of the alkoxyamines with LiAlH4gave the corresponding chiral amines. The diastereoselectivity of the reaction appears to directly mirror theE:Zratio of the starting oxime ethers.

ISSN:0008-4042    

DOI:10.1139/v93-108

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Aluminum present in pooled samples of cerebrospinal fluid is essentially uncomplexed since it may be determined by differential pulse polarography of the Al: Solochrome Violet RS (SVRS) complex. The aluminum may also be determined spectrophotometrically through its depression of the SVRS absorbance at 600 nm at pH 8.4. The Al:SVRS ratio in the complex is 1:2.

ISSN:0008-4042    

DOI:10.1139/v93-109

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The Diels–Alder cycloaddition reaction of the fumarate of methyl lactate or methyl mandelate with α-hydroxy-ortho-quinodimethane produces an unexpectedexoproduct with very high asymmetric induction. Experiments and calculations have been carried out that show that the origin of the stereoselectivity in these reactions is related to hydrogen bonding between the α-hydroxy-o-quinodimethane and the lactate or mandelate group in the dienophile.

ISSN:0008-4042    

DOI:10.1139/v93-110

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

Selenium in anodic slime is determined by using an indirect method. Selenite is reduced by ferrous iron, the ferric iron formed is complexed with KSCN, and the absorbance at 480 nm is measured. In this way selenium (10−3–10−2 M) can be determined in the presence of copper and tellurium without any separation.

ISSN:0008-4042    

DOI:10.1139/v93-111

出版商:NRC Research Press    

年代:1993

数据来源: NRC

摘要:

The X-ray structures of four dioxolan-2-ylium cations, 2-phenyl-1,3-dioxolan-2-ylium trifluoromethanesulfonate,6, and 2-(4-methoxyphenyl)-1,3-dioxolan-2-ylium,7, 2-(2,4-pentadienyl)-1,3-dioxolan-2-ylium,8, and 2-(4-methoxyphenyl)-4,4-dimethyl-1,3-dioxolan-2-ylium,9, hexafluoroantimonates, have been determined. Crystals of6are monoclinic,C2/c,a = 28.934(5),b = 6.022(2),c = 14.831(3) Å, β = 113.37(1)°,Z = 8; 1944 reflections were used to determine the structure;R = 0.0488,wR = 0.0477. Crystals of7are monoclinic,P21/c,a = 11.948(4),b = 10.686(3),c = 10.853(2) Å, β = 106.31(2)°,Z = 4; 2260 reflections were used to determine the structure;R = 0.0551,wR = 0.0807. Crystals of8are monoclinic,P21/c,a = 10.549(2),b = 10.457(3),c = 11.702(2) Å, β = 105.69(1)°,Z = 4; 2190 reflections were used to determine the structure;R = 0.0337,wR = 0.0299. Crystals of9are orthorhombic,Pmnb,a = 8.297(4),b = 15.269(3),c = 12.638(2) Å,Z = 4; 1736 reflections were used to determine the structure;R = 0.0796,wR = 0.0726. Intensities were measured on Syntex P21, or Nicolet P3 diffractometers at −65 °C with use of Mo Kα radiation. These structures are discussed in terms of the conjugation and charge distribution in these cations. In each case the cations are almost planar with very small twist angles between the plane of the C(2) substituent and that of the dioxolanylium ring. Cation8is the first reported example of the structure determination of an acyclic, substituted dienyl carbenium ion. The unsaturated five-carbon chain in8has an all-transconformation about all the C—C bonds, but, apart from the C(2)—C(1′) distance, none of the other bond distances differ significantly from those found in corresponding neutral systems. The C(2)—C(1′) distance in7is significantly shorter than that of6, suggesting enhanced conjugation of the aryl ring with the positive centre in the former cation. This suggestion is supported by the significant quinonoid-type distortion that is observed in thep-methoxyphenyl ring of7. Systematic variations in the O(1)—C(5)/O(3)—C(4) bond distances are examined and it is shown that alkyl substitution at C(4)/C(5) leads to a large increase in their lengths, suggesting that the presence of a significant fraction of the positive charge is located on C(4) and (or) C(5). Support for this suggestion is found in a large variety of previously reported spectroscopic and calorimetric measurements.

ISSN:0008-4042    

DOI:10.1139/v93-112

出版商:NRC Research Press    

年代:1993

数据来源: NRC