Oxidants nitrobenzene

Related Compounds. LXXV. Alkaline Nitrobenzene Oxidation of Plant Materials and Application to Taxonomic Classification. J. Amer. chem. Soc. 66, 32 (1944). 

Rapid Micromethod for Alkaline Nitrobenzene Oxidation of Lignin... 

Certain derivatives of the lignin sulfonic acids can be determined directly in water. The nitroso derivatives, which are easily formed in solution, can be determined by differential pulse polarography [438]. Vanillin can be formed by alkaline hydrolysis [439] or alkaline nitrobenzene oxidation [440], extracted into an organic solvent and determined by gas chromatography. 

Nitrobenzene oxidation was carried out by adding 50 mg of dry soda lignin into a mixture of 7 mL of 2 M NaOH and 4 ttiL of nitrobenzene in a 15 ttiL steel autoclave. Then, the antoclave was heated to 165°C for 3 hours in a preheated thermostat oil bath. After the autoclave was cooled to room temperature, the mixture was then transferred to a liqnid-hquid extractor for continuous extraction with chloroform (5 x 20 mL) in order to remove any nitrobenzene reduction product and excess nitrobenzene. The oxidation mixtnre was then acidified by concentrated HCl to pH 3 and further extracted with chloroform (5x15 mL). The solvent from the second chloroform solution was then removed using a rotary evaporator at 40°C under reduced pressure in order to obtain the nitrobenzene oxidation mixture. The mixture was then dissolved into dicloromethane and made up to 10 luL. This mixture was then used as a stock solution for high performance liquid chromatography (HPLC) analysis [6]. 

The nitrobenzene oxidation mixture was analyzed using the HPLC method. 0.2 mL of the stock solution was pipetted into a 25 mL volumetric flask and acetonitril-water (1 2 vA ) was added to it. About 20 gL of the sample solution was next injected into the HPLC system (Shimatzu) equipped with a Hypersil bond C,g coluitm (particle size 5 gL, 25 x 4.6 mm i.d.) to quantitatively determine the vanillin component while another component was determined qualitatively. Acetonitril-water (1 8) containing 1% acetic acid was used as an eluent with a flow rate of 2 tuL/min. The eluent was then monitored with an UV (ultraviolet) detector at 280 ran [6]. 

The nitrobenzene oxidation product was used in this process [13]. The mixture was dissolved into acetone and made up to 10 mL. Next, the mixture was heated to 60°C for 10 minutes using a hot plate. The precipitate was then filtered and washed using... 

Condensed Structures in p-Hydroxyphenyl-Guaiacyl Type DHP. It has been difficult to determine the exact amount of p-hydroxyphenylpropane units in lignin. This can best be illustrated by an example nitrobenzene oxidation of a DHP prepared by the Zutropfverfahren method from a mixture of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, gave no detectable p-hydroxybenzaldehyde on alkaline nitrobenzene oxidation... 

Table V. Molar Ratios of p-Hydroxyphenyl (H) to Guaiacyl (G) Units in DHP s and their Nitrobenzene Oxidation Products...

Figure 2. Dehydrogenative polymerization of a mixture of p-coumaryl alcohol-[ring-2-3H] and coniferyl alcohol-[U-14C], and nitrobenzene oxidation of the DHP to give p-hydroxybenzaldehyde-[ring-2-3H] and vanillin-[formyl-14C].

As can be seen, the molar ratios of p-hydroxyphenyl to guaiacyi units were slightly lower for the DHP s when compared to the original mixtures. This implies that coniferyl alcohol tends to be incorporated into the polymer slightly more readily than p-coumaryl alcohol. On the other hand, the much-reduced ratio of p-hydroxybenzaldehyde to vanillin, liberated during alkaline nitrobenzene oxidation, proved that this DHP contained a larger amount of condensed p-hydroxyphenylpropane units than condensed guaiacyi units. 

Table II. Lignin Monomer Composition, Obtained by Nitrobenzene Oxidation of Lignin from Normal and Brittle Fescue Grown at Lusignan (Same as in Table I)...

Tables IV and V show the monomer composition of lignins for both parietal and saponification residues. In this regard, comparison between PR and SR values allows the characterization of the lignin core, which is not solubilized after alkaline treatment (20,21). Instead of using nitrobenzene oxidation, thioacidolysis was used to characterize the non-condensed...

Enough heat is generated by the reaction to keep the suspension at boiling point. It is essential to have an excess of iron metal to ensure complete decomposition of the nitrobenzene. The details of the reaction mechanism are not fully understood, but it is presumed that the nitrobenzene oxidizes Ee to Ee which is then hydrolysed. The acid is released by hydrolysis and pigment formation and dissolves the metallic iron and thus renews the supply of Ee " no additional acid other than that produced dur-... 

Information obtained from the systems studied, leads to the assumption that the time dependence of the product distribution of selective nitrobenzene oxidation (fig.l) has to be explained in the following way ... 

Aromatic aldehydes and ketones have been extensively reported from alkaline nitrobenzene oxidations but not from oxygen or nitric acid oxidations. A number of nitrophenols and nitrated aromatic acids have been... 

Alkaline Nitrobenzene. Conditions of alkaline nitrobenzene oxidation of wood or lignin reported by Leopold (33) have been used throughout this work. The standard conditions used include ... 

Results of the previously described semiquantitative method of analysis, applied to methyl enters, are reported in Table V. Yields of products eluting before methyl benzoate have not been included in this table since these should be included in the results presented in Table III. Total yield of methyl esters was largest in the neutral oxygen oxidation, slightly lower under alkaline oxygen oxidation, and substantially lower in acidic oxygen, nitric acid, and alkaline nitrobenzene oxidations. The differences in yields may be attributed in a large part to three major peaks phthalate, a component at a relative retention time of 0.490, and benzoate. 

The ratio of vanillin to vanillic acid and the yields of these two products, expressed as percentages of wood lignin, are the most significant data available to judge the severity of an alkaline nitrobenzene oxidation of a coniferous wood. The yields of vanillin and vanillic acid reported in Tables IV and V as methyl ether and methyl ether ester are only approximately 8 and 50%, respectively, of amounts that might be expected based on previous work. The ratio of vanillin to vanillic acid has been found to be 8 1 whereas in the reaction reported here it is 1 2. Furthermore, Leopold 32) reported vanillin vanillic acid oxalic acid as 6 1 2 whereas... 

An example of the use of the nitrobenzene oxidation to elucidate differences in lignin subunit composition between wild-type and mutant Arabidopsis plants can be found in Chappie et al. (1992). They dried and ground stem tissue of Arabidopsis and extracted 50 mg with methanol (three times 1 mL) and deionized water (twice, 1 mL) at 60°C. Esterified phenolics... 

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