MARCH
19G2
I n work to be described elsewhere,6 the disulfide I11 has been studied as a free radical initiator and as avulcanizing agent for natural and synthetic rubber. I n contrast with AIBN, which decomposes rapidly compound IT1 appears to between 60 and be an effective radical source only above 150'. EXPERIMENTAL7
Reaction of AIBN with sulfur. In a 1-1. flask fitted with an oil bath heater and a reflux condenser were placed 16.4 g. (0.100 mole) of AIBN, 25.6 g. (0.100 mole) of sulfur and 500 ml. of reagent grade benzene. Heating the mixture to reflux gave a clear yellow solution. After 21/2 hours of reflux a second 16.4-g. portion of AIBN was added and reflux continued for another 16 hr. (about 14 half-lives of AIBNB). The reaction mixture waa then freed of benzene by distillation and taken up in 150 ml. of methanol. Filtration of the methanol slurry removed 17.3 g. (67.6%) of unreacted sulfur, m.p. 116.5-117.5'. The filtrate waa evaporated to dryness to give 30.2 g. of yellow crystalline solid VII, m.p. 35-1 15'. Separation of products formed in reaction of AIBN and sulfur. A 3.5 x 17-cm. column waa packed with 140 g. of Brockmann grade 1 activated aluminas and wet with 105 ml. of 5% reagent ether in reagent pentane. After washing the column with an additional 100 ml. of this solvent, 1.5 g. of VI1 in 30 ml. of 5% ether in pentane waa introduced. The following fractions were then eluted.
Fraction
a b C
d e f g h 1
j
k
1 m n 0
P r 8
t U
1079
NOTES
Pentane Eluent M1. % Ether 75 5 75 5 110 5 110 10 110 10 110 25 110 25 110 25 110 50 150 50 150 50 150 50 150 100 150 100 150 100 150 100 150 100 150 100 300 100 300 Methanol 100 Methanol
Residue after Evaporation of Solvent, G. None 0.05 yellow solid 0.05 yellow solid None 0.0050il 0.005 oil 0.025 white solid 0.025 white solid 0.10 white solid 0.10 white solid 0.02 white solid 0.02It. yellow oil 0.10 It. yellow oil 0.10 It. yellow oil 0.05 white solid 0.02 It. yellow oil 0.02 It. yellow oil 0.01 It. yellow oil 0.01 It. yellow oil 0.35 yellow oil None
The various fractions were combined and characterized as follows: b and c, 0.10 g. (8%) of unchanged sulfur as yellow granules, m.p. 112-115', lit. valueg for rhombic form, 112.8'; g through k, 0.27 g. (20%) of I, tetramethyl-
succinonitrile, aa white plates, m.p. 158-161 ', lit. valuela 167'; m, n, p, and p were seeded by o to give a total of 0.31 g. (16%) of 111, 2,2'-dithiobisisobutyronitrile, as white granules, m.p. 50-59'; and r through t, 0.37 g. of higher sulfides IV as yellow oil. The remainder of the crude reaction product VI1 was chromatographed on a 5.7 X 100-cm. column packed to a depth of 76 cm. with 1570 g. of Brockmann grade 1 activated alumina. The 6.5 g. of cmde 2,2'-dithiobisisobutyronitrile so obtained waa recrystallized from 50% ether in pentane to give 5.0 g. of pure 111, m.p. 63-64'. Anal. Calcd. for CSH12N&: C, 47.96; H, 6.04; N, 13.98; S, 32.02. Found: C,48.11; H, 5.85; N, 13.87; S, 32.22. The infrared absorption spectrum of I11 showed peaks a t 2960, 2910 and 2850 cm.-l (aliphatic C-H), 2220 cm.-l ( C d ) , 1445 and 1364 cm.-' (aliphatic C-H), 1205 and 1155 cm.-l (isopropyl group), and 770 cm.-' (weak, disulfide). Hydrolysis of B$'-dithiobisisobutyronitrile. Five grams (0.025 mole) of I11 waa heated with stirring for four houn a t 100' with 25 ml. of 75oj, sulfuric acid and 1 g. of sodium chloride. The reaction mixture was cooled to room temperature and poured onto 100 g. of ice. The white precipitate waa separated and largely dissolved by 15 ml. of 5% sodium hydroxide. After filtration to remove a small amount of white solid, the clear solution was run into 20 ml. of 20% hydrochloric acid. The white solid was separated, dried and recrystallized from 1:1 acetone-water to give 2.0 g. (34y0) of 2,2'-dithiobisisobutyric acid as white crystals, m.p. 157-158'. Anal. Calcd. for CsH1404S2: C, 40.32; H, 5.92; S, 26.85. Found: C, 40.58; H, 6.13; S,26.92. RESEARCH CENTER UNITEDSTATESRUBBERCOMPANY WAYNE,N. J. (10) A. F. Bickel and W. A. Waters, Rec. trav. chim., 69, 1490 (1950).
Composition of Peat Humus and Its Derivatives. Oxidative Conversion to Lignin Model Compounds HIROEAZU MORITA Received September 11, 1961
The organic chemistry of one of the most ubiquitous natural products, soil humus,' remains enigmatic despite its early origin. The biogenesis of humus has been a t t r i b ~ t e d ~to - ~ the microbial decomposition of plant and bacterial tissues in the soil. The resulting organic material contains lignin derivatives, proteins, carbohydrates, waxes, organic acids, and other unidentified compounds.
(1) A prospectus of humus research will be presented elsewhere. (5) D.I. Relyea (to U.S. Rubber Co.), U. S. and foreign (2) S. A. Waksman, Humus, Bailliere, Tindall and Cox, patents pending. London, 1936. - (6) F: M. Lewis and M. S. Matheson, J. Am. Chem. SOC., (3) E. J. Russell and E. W. Russel, Soil Conditions & Plant 71.747 (1949). Growth, 8th edition, Longmans, Green and Co., New York (7) Ail melting points are corrected. 1950, Chapter 15. (8) H. Brockmann and F. Volpers, Ber., 80, 77 (1947). (4) J. M. Bremner, J. Soil Sn'., 5, 214 (1952). (9) Handbook of Chemistry and Physics, 32nd ed., Chem. (5) H. Thiele and H. Kettner, Kolloid Z., 130, 1310 Rubber Publ. Co., Cleveland, 1951, p. 578. (1953).
1080
VOL. 27
NOTES
TABLE Ia PAPER CHROMATOGRAPHIC ANALYSIS OF LIGNINOXIDATION PRODUCTS Compound
Rf
Yieldb
Compound
Rf
Yieldb
0.72 0.68 0.63 0.50
0.03 0.15 0.03 0.46
5-Carboxy vanillin p-Hydroxybenzoic acid Vanillic acid Syringic acid
0.39 0.38 0.34 0.30
0.09 1.85 0.95 0.31
~
Acetovanillone p-Hydroxybenzaldehyde Acetosyringone Vanillin a
Descending development on Whatman No. 1 filter paper wit,h butanol-ethanol-2% aq. ammonia (160:40:90). Yield in
% based on ash-free weight of peat soil.
We have been studying the composition of certain agriculturally important soils derived from peat as a starting model for our general research program on soil organic matter. Specifically, we have carried out selective oxidative degradation of artificially decomposed peat with a view to determining the constitution of peat lignin derivatives. In this note we wish to report some important qualitative data. Despite certain reservations, it is generally conceded that the primary structural elements of lignin are derived from p-hydroxyphenyl, guaiacyl, or syringyl units.6 These units are also to be found when peat soil derived from Sphagnum is oxidized by mercuric oxide in boiling alkali. I n the current theme of soil humus biogenesis, the lignin or lignin derivatives are considered to to be the most refractory of plant tissues. Our evidence shows that in peat soils where decomposition has been artificially promoted by the addition of lime, the lignin derivatives still retain their aboriginal microstructure. Our evidence further suggests the intriguing prospect of fractionating the lignin-humic complexes from soil organic matter by the use of commercial preparative methods-for example, the synthesis of lignosulfonic acids. This aspect of our work will be reported in due course. EXPERlMENTAL
Sampling. The soil samples were obtained from Sphagnum peat farms located a t Alfred, Ontario, which have been under cultivation for the last six years. Before cultivation the peat fields were treated with lime to reduce the acidity and to accelerate the “humification” of the organic matter. Samples were taken at predetermined spote at depths of from 6 to 18 inches. They were air-dried, finely ground, and extracted with benzene-ethanol (2:l) mixture using a Soxhlet apparatus. Elemental analysis gave 53.25% C, 61.48% H, 1.90% N, 2.38% methoxyl, and 8.37% ash. Proximate analysis showed 21% lignin-humic complexes.’ Ozidation. The procedure is essentially that described by Pearl.* A 30-g. sample of peat soil was treated with 271.5 g. (1 mole) of mercuric chloride, 200 g. (5 moles) of sodium hydroxide in 1250 ml. of water. The reaction mixture was heated under reflux with stirring for 8 hr., acidified with sulfur dioxide and extracted with ether. The aqueous residue was further acidified with 45% sulfuric acid and (0) F. E. Brauns, The Chemistry of Lignin, Academic Press Inc., New York, 1952. (7) Material insoluble in 72% sulfuric acid, cf. Tappi Standard T-lzm Method. (8) I. A. Pearl, J . Am. Chem. Soc., 71, 2196 (1949).
exhaustively extracted with ether. The ether soluble materials were subsequently divided into 21% sodium bisulfite, 8% sodium bicarbonate, and 5% sodium hydroxide soluble fractions. The ether solutions were dried over anhydrous sodium sulfate and concentrated to 25 ml. Aliquot samples were then used for paper chromatographic analysis. The yields of the bisulfite-, bicarbonate-, and alkalisoluble fractions based on ash-free organic matter were 9.8%, 6.0%, and 4.8%, respectively. The positive identification, isolation, and quantitative analyses of the oxidation products listed in Table I were accomplished by established paper chromatographic technique~.~-’* The aggregate yields of the compounds based on spectrophotometric estimation was 4.07% calculated on the ash-free weight of the peat soil. For a general survey of the ether soluble peat oxidation products the most useful descending paper chromatographic solvent was found to be butanol-ethanol-2% aqueous ammonia (160:40:90 v/v). The Rr values of some pertinent compounds are listed in Table 1. The appropriate chromogenic reagents have appeared in the literature.l* With our ammoniacal solvent, the detection and quantitative isolation of the components in mixtures containing p-hydroxybenzaldehyde, acetovanillone, and acetosyringone could not be readily accomplished. Reliable results were, however, achieved by the use of borate buffered paper.1° Similarly, the presence of bcarboxyvanillin interfered with the analysis of p-hydroxybenzoic acid and vanillic acid. In this instance, papers impregnated with a phosphate buffer a t pH 7.4 afforded a convenient alternative method.” CANADA DEPARTMENT OF AGRICULTURE OTTAWA,CANADA (9) I. A. Pearl, D. L. Beyer, B. Johnson, and S. Wilkinson, Toppi, 40,374 (1957). (10) D. E. Bland and C. Stamp, Australian J . AppZ. Sci., 6,353 (1955). (11) B. Leopold, Acta Chem. Sand., 6 , 38 (1952). (12) J. L. Gardon and B. Leopold, Pulp Paper Mag. Can., 57, T-148 (1958). (13) I. A. Pearl and P. F. McCoy, Anal. C h a . , 32, 1407 (1960), and ref. 9 to 12.
Utility of the Methanesulfonyl Blocking Group. 111. A New Synthesis of Dimesyl Protocatechuic Acid1Ia J. H. LOOKER,JAMES H. MCMECHAN, AND YEN-LUNQ HUNQ
Received September 1.6, 1961
A synthesis of dimesyls protocatechuic acid (11) from dimesyl protocatechualdehyde has been pre(1) J. H. Looker, J . Org. Chem., 24, 1039 (1959). (2) This investigation waa supported by a research grant (CY-4750) from the National Cancer Institute, Public Health Service.
