摘要:

The research confirmed the fact that chlorine dioxide and sodium chlorite were not equivalent in their oxidizing properties. At 22 °C. or less, the oxidation of pyrogallol by aqueous sodium chlorite at pH 6 was very slow, but became very rapid on the acid side of pH 3.5. The amorphous, colored products probably did not include purpurogallin. Under similar circumstancesp-hydroxybenzaldehyde was unaffected at pH 6; 22% was oxidized top-benzoquinone (Dakin's reaction) at pH 5, and this amount increased to 39% at pH 1. The yield of benzoquinone was about 24% regardless of pH within the above range when aqueous chlorine dioxide was the oxidant. Sodium chlorite at pH 0.9 produced a 91% yield of methoxy-p-quinone from methoxy-p-hydroquinone; at pH 4 this product was mixed with 56% of 4,4′-dimethoxydiquinone, but near pH 6 a slower oxidation did not proceed beyond 4,4′-dimethoxyquinhydrone. Aqueous chlorine dioxide yielded at least 92% of monomeric methoxyquinone at all pH values between 1 and 6, probably in accord with the equation,The simultaneous formation of hydrogen peroxide was suspected, but not proved. In sharp distinction to the behavior of free phenols, veratraldehyde was not oxidized by aqueous chlorine dioxide between pH 6 and pH 3, but at pH 1 a slow reaction yielded up to 15% of veratric acid. Sodium chlorite produced about 92% of the same acid at pH 1 and pH 4, but its action was negligible at pH 5. Since by-product chlorine dioxide was ineffective at pH 4, it was possible to confirm the validity of the Jeanes–Isbell equation for the reduction of chlorous acid:The oxidation of acetylated vanillin was complicated by the occurrence of deacetylation. Red, chlorinated oils with quinoidal properties were also formed in most of the above oxidations.

ISSN:0008-4042    

DOI:10.1139/v55-011

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v55-012

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v55-013

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The rates of exchange of acetate—concurrent with anomerization—between the C1-acetoxy groups of the pentaacetates (0.05 M) ofD-glucose andD-mannose and stannic trichloride acetate (0.05 M) in chloroform containing stannic chloride (0.05 M) were determined at 40 °C. using isotopically labelled acetate. 1,2-trans-α-D-Mannose pentaacetate underwent exchange seven times more rapidly than the β-1,2-cis-anomer but eight times less rapidly than 1,2-trans-β-D-glucose pentaacetate. The latter compound was 450 times more reactive than the α-1,2-cis-anomer. In accordance with these results, theD-mannose pentaacetate underwent mercaptolysis in ethyl mercaptan containing zinc chloride at rates intermediate to those found for theD-glucose pentaacetates. The main product from the mannose pentaacetates was in each case ethyl 1,2-trans-α-D-1-thiomannopyranoside tetraacetate (60–70% yield). Tetra-O-acetyl-β-D-glucopyranosyl chloride with silver acetate gave β-D-glucose pentaacetate when the reaction was carried out in dry acetic acid but gave 2,3,4,6-tetra-O-acetyl-α-D-glucose in 90% aqueous acetic acid. Tetra-O-acetyl-β-D-glucopyranosyl chloride with methanol and silver carbonate gave a sirupy product with the properties expected for methyl 1,2-ortho-O-acetyl-α-D-glucopyranose triacetate. The substance was hydrolyzed by 0.005 Nhydrochloric acid in 95% dioxane 18 times more rapidly than the corresponding derivative of β-D-mannose. The significance of these observations toward an understanding of the effect of configuration on reactivity is discussed.

ISSN:0008-4042    

DOI:10.1139/v55-014

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

Unequivocal evidence that the anomerization of acetylated alkyl glycopyranosides can proceed by way of an intramolecular mechanism was obtained through the observation that a racemic mixture of methyl β-glucopyranoside tetraacetate with theD-isomer labelled in the methoxyl group with carbon-14 is anomerized both by titanium tetrachloride and boron trifluoride without transfer of radioactive methoxyl groups to theL-isomer. It is submitted that these intramolecular anomerizations are best rationalized as the result of an unsuccessful attempt by the environment to bring about glycosidic cleavage and proceed by way of an ion-pair intermediate in which the anion is derived from the aglycon group.

ISSN:0008-4042    

DOI:10.1139/v55-015

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

3,4,6-Tri-O-acetyl-β-D-glucopyranosyl chloride was found to undergo solvolysis in acetic acid to form 1,3,4,6-tetra-O-acetyl-α-D-glucopyranose as the main reaction product. The much less reactive anomeric α-chloride also appeared to undergo solvolysis with extensive inversion of the anomeric center. It is submitted that the tendencies for inversion obtained in these ionic reactions are due to the conformations imposed on the intermediate ions through distribution of the positive charge to the ring oxygen and the consequent introduction of double-bond character to the carbon-1 to ring-oxygen bond.

ISSN:0008-4042    

DOI:10.1139/v55-016

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The effects were studied of substituting one, two, and three chlorine atoms at the C2-acetoxy group of the α- and β-D-glucopyranose pentaacetates on the rates both of anomerization and of dissociation of the C1 to acetoxy group bond in 1:1 acetic acid – acetic anhydride 0.5 Mwith respect to sulphuric acid at 25 °C. In the case of the α-anomers, the rates of anomerization appeared about equal to the rates of dissociation as measured by isotopic exchange. The β-anomers dissociated more rapidly than they underwent anomerization. The difference in rate decreased rapidly, however, with the introduction of chlorine atoms indicating that the tendency for C2-acyl group participation in the dissociation is reduced by the chlorine substitutions. Evidence was obtained that only a very small fraction, if any, of the C1-acetoxy group of β-glucose pentaacetate passes into the α-anomer without becoming completely dissociated. It is pointed out that the data for the anomerizations can be rationalized on the basis of ionic mechanisms, if specific conformations are allocated to the intermediate carbonium ions.

ISSN:0008-4042    

DOI:10.1139/v55-017

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

The acetolyses of thealphaandbetamethylD-glucopyranoside tetraacetates in 1:1 acetic acid – acetic anhydride 0.5 Mwith respect to sulphuric acid were followed at 25 °C. by isotopic dilution analysis of products isolated after various intervals of time. The reaction of the α-glucoside was found to proceed mainly with inversion of the anomeric center. On the other hand, the β-glucoside was found to undergo acetolysis with retention of configuration concurrent with anomerization. It was shown that the polarimetric changes observed in the course of the reactions could be satisfactorily accounted for on the basis of these reaction routes. Reaction mechanisms are suggested.

ISSN:0008-4042    

DOI:10.1139/v55-018

出版商:NRC Research Press    

年代:1955

数据来源: NRC

摘要:

not available

ISSN:0008-4042    

DOI:10.1139/v55-019

出版商:NRC Research Press    

年代:1955

数据来源: NRC