Determination of Formula Unit for a Compound Zinc Powder and Hydrochloric Acid - PDF by zju20190

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									                          THE     CHEMISTRY                OF LIGNIN
                           X. LIGNIN        FROM        OAT        STRAW*

                      BY    MAX        PHILLIPS         AND    M.    J. GOSS
(From     the Industrial  Farm Products     Research Division,    Bureau   of Chemistry
        and Soils, United    States Department      of Agriculture, Washington)
                      (Received for publication April 20,                   1936)

    In a previous communication      (1) results of an investigation were
presented dealing with the chemistry of ligqin from barley straw.




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A review of the literature was then presented.             Inadvert,ently,
reference to a paper by Marion (2) dealing with the lignin of oat
and wheat straws was then omitted.
    In this paper results of a study of the lignins from oat straw are
presented.      Three lignin fractions were isolated from oat straw.
The first two fractions were isolated by successive and exhaustive
extractions,    first with a 2 per cent alcoholic sodium hydroxide
solution at room temperature, and then by refluxing with a 4 per
cent aqueous sodium hydroxide solution, according to the method
previously described (1). The third fraction was isolated from
the straw remaining from the extraction operations referred to
above with fuming hydrochloric          acid. The composition of the
first lignin fraction agreed with that represented by the formula
C40H48015. On the basis of a compound having a molecular weight
represented by this formula, approximately          four methoxyl groups
and four hydroxyl groups were shown to be present.             Of the four
hydroxyl groups, two could be methylated              with diazomethane,
thus indicating that these are more acidic, possibly phenolic or
enolic in character.      On methylation      with dimethyl sulfate and
sodium hydroxide solution (9 per cent) incomplete methylation
of the four hydroxyl groups resulted.           However, by remethylat-
ing this preparation with dimethyl sulfate and 40 per cent sodium
hydroxide solution, a product was obtained containing five meth-
oxyl groups in addition to those naturally present in this lignin
   * Industrial    Farm     Products     Research       Division      Contribution   No.   260.
                                                  557
558                 Chemistry        of Lignin.      X
fraction, thus indicating that this drastic treatment resulted in the
formation of one more hydroxyl group which was then methylated
by the dimethyl sulfate.
   When this lignin fraction was subjected to fusion with potassium
hydroxide,    protocatechuic     acid (isolated as its dimethyl       ether,
veratric acid) in approximately        4 per cent yield was obtained.
   The analytical results on the second lignin fraction are more
in agreement with those represented by the formula CMHUOS
In this lignin fraction approximately          four methoxyl groups and
four hydroxyl      groups were shown to be present.           Two of the




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hydroxyl groups could be methylated with diazomethane.
   The methoxyl content of the third lignin fraction was found to
be about the same as that of the other two lignin fractions.           This
lignin fraction was found to contain a higher percentage of carbon
than either of the other two lignin fractions.
   By means of a method previously             described (3), the alkoxyl
groups in the three lignin fractions were shown to be methoxyls.
The presence of other alkoxyl groups, such as, for example, ethoxyl
groups, was definitely excluded.
   The three lignin fractions when distilled with 12 per cent hydro-
chloric acid afforded small quantities            of formaldehyde.      The
significance of the isolation of this fission product from lignin from
the standpoint of the presence of a methylene dioxide group in
this substance has already been discussed in the paper referred
to (1).
    In comparing the lignin fractions isolated from oat straw with
the corresponding      lignin fractions isolated from barley straw one
is led to the conclusion that, if these lignins are not identical, they
are certainly closely related.

                             EXPERIMENTAL

   1 kilo of ground oat straw (910 gm. of moisture-free    material)
was subjected to an exhaustive       extraction  with an alcoholic
sodium hydroxide solution according to the procedure described
in a previous communication      (1). The crude lignin thus ob-
tained, after being dried in a desiccator       over sulfuric acid,
amounted to 61 gm. (6.7 per cent yield calculated on the weight
of dry straw taken).    The weight of the straw which had been
extracted with 6he alcoholic sodium hydroxide solution was 855
                  M. Phillips and M. J. Goss
gm. (dry weight).     The crude lignin was treated with 1 liter of an
acetone-alcohol solution (2 volumes of acetone to 1 volume of 95
per cent ethanol), the lignin solution was filtered, and the alcohol
and acetone were removed by distillation under reduced pressure.
The lignin thus obtained was washed with water and dried at 56”
over phosphorus      pentoxide in the vacuum Abderhalden            drier.
The yield of this purified lignin amounted to 30 gm. (3.3 per cent
calculated on the weight of dry straw taken).     The lignin obtained
was a light tan amorphous powder.           A carbon and hydrogen
determination    made upon the lignin gave the following results:




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 Found, C 62.6, 62.5, H 6.2, 6.1.
   The lignin gave no test for furfural with aniline acetate paper
when distilled with 12 per cent hydrochloric     acid.
   The nature of the alkoxyl group present in this lignin fraction
was established by the method of Willstatter        and Utzinger (4).
The crystalline trimethylphenylammonium         iodide was identified
by its melting point and mixed melting point.        In order to prove
definitely that no alkoxyl groups other than methoxyl are present
in this lignin fraction, the method described by one of us in a
previous communication        (3) was used. Found, (Zeisel method)
OCHI 14.76, 15.04, (Kirpal and Biihn method) 14.84, 14.88. The
ratio of the percentage of total carbon to the percentage of carbon
present in the form of methoxyl is 10.8:1.
   The data obtained on the percentages of carbon and hydrogen in
this lignin fraction agree with the percentage composition              as
represented by a compound of the empirical formula C%~H~~OE,.
The calculated percentages are C 62.50, H 6.25. The percentage
of methoxyl found in this lignin fraction is somewhat low as com-
pared with that calculated for four methoxyl groups in a com-
pound represented by the above formula.         The results obtained
correspond to 3.7 methoxyl groups in every unit represented
by the above formula.
   Distillation with 19 Per Cent Hydrochloric         Acid-2     gm. of
lignin were distilled with 12 per cent hydrochloric         acid by the
procedure recommended by the Association          of Official Agricul-
tural Chemists for the determination of pentosans.        The distillate
was neutralized with sodium bicarbonate, then made slightly acid
with acetic acid, and redistilled, and the first 50 cc. of distillate
were retained.     This distillate was treated with an alcoholic
                     Chemistry       of Lignin.        X

solution of dimethylcyclohexanedione,             as suggested by Wein-
berger (5). The crystalline        precipitate     was recrystallized     from
dilute alcohol, m.p. 191-192”, mixed m.p. 191-192”.            The presence
of formaldehyde         in the distillate      was, therefore,      definitely
established.
     Alkali Fusion-To      50 gm. of potassium hydroxide contained in
a nickel crucible, 25 cc. of water and 10 gm. of zinc dust were added
and the mixture was heated to 100”. To these were added por-
tionwise 5 gm. of lignin while the reaction mixture was stirred.
The temperature of,the mixture was gradually raised to 250” and




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maintained at that temperature for 30 minutes.            The reaction was
completed by heating the mixture at 310” for 15 minutes.                    The
melt was allowed to cool and then dissolved in water, filtered,
acidified with dilute sulfuric acid, and distilled in a current of
steam until the distillate no longer gave an acid reaction.                The
total distillate was titrated with 0.1 N sodium hydroxide solution,
phenolphthalein       being used as the indicator.          181 cc. of the
alkali were required.       The entire neutralized distillate was evapo-
rated to dryness on the steam bath.               The acid p-toluide was
prepared according to the method of Mulliken             (6). The toluide
melted at 148%149”, and, when mixed with some pure acet-p-
toluide, there was no depression in the melting point.               The acid
was, therefore, acetic acid.
     The solution remaining in the distilling flask was filtered and the
filtrate was repeatedly extracted with ether.            After removal of
the ether a dark brown syrup was obtained.             To this were added
25 cc. of 10 per cent sodium hydroxide solution, followed by 10 cc.
of dimethyl sulfate.       The methylation was completed by warming
the reaction mixture on the steam bath.            The cooled solution was
extracted with ether and after removal of the ether a small
quantity of syrup was obtained which had the odor of veratrole.
The amount obtained was insufficient for identification.
     The alkaline solution which had been extracted with ether was
acidified with hydrochloric      acid and again extracted with ether.
After removal of the ether a gummy residue was obtained.                  This
was boiled with water, decolorized with norit, filtered, and con-
centrated.      Crystals were obtained which, after three recrystalli-
zations, melted sharply at 180-181” (corrected).               When mixed
with some pure veratric acid, no depression in the melting point
                         M. Phillips and M. J. Goss                                                     561

was observed.      The yield of pure material amounted to 0.2 gm.
 = 4 per cent of the weight of lignin.
   Acetylation-The    lignin was acetylated by the method described
in a previous investigation    (7). The product, light gray in color,
was dried at 56’ in the Abderhalden          drier over phosphorus
pentoxide.
  Andysis-
                                 (OCHA
                         /
           Cadh.On                                Calculated.      CH9aCO            18.3




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                         \
                                 (CO.C&h
                                                                         ‘I
                                                  Found.                             18.1, 18.0

   The percentage of acetyl was determined        by the method
described by one of us (8).
   Chlorination-The    chlorination  of this lignin fraction   was
carried out as described in a previous communication      (7). The
product was colored lemon-yellow.
  Analysis-
      CaoH,O&lw                  Calculated.        Cl 42.98,                 OCH9     9.40
                                 Found.             “ 43.28,    43.45,          “      7.07,   7.07

   It will be noted that there was a loss of methoxyl brought about
by the chlorination.     A similar observation     has been made in
connection with the bromination of lignin from spruce wood (9).
   Methylation with Diazomethane-2       gm. of lignin were added to
an ether solution containing approximately     2 gm. of diazomethane
and the mixture allowed to stand at room temperature              with
occasional stirring for 5 days. The product was filtered off, air-
dried, and finally dried in vacua at 56” over phosphorus pentoxide.
A light tan amorphous product was obtained.
  Anulysis-
                                 (OCHda
                             /
              C39H3409                         Calculated.      OCHI      23.36
                         \
                                 (OCH&
                                               Found.              “     23.51,       23.50

   The methylation    with diazomethane    was                                  repeated          but   no
increase in the methoxyl content was obtained.
                      Chemistry      of Lignin.       X

    Methylation with Dimethyl Suljate-3      gm. of lignin were dis-
solved in a solution containing 10 gm. of sodium hydroxide in 100
cc. of water, and 24 cc. of dimethyl sulfate were added drop by
drop, and the reaction mixture was stirred mechanically.       After
all the dimethyl sulfate had been added, the reaction mixture
was heated on the steam bath for 30 minutes.       The product was
filtered off, washed with water, and dried over phosphorus pent-
oxide. A methoxyl determination          gave the following  results:
Found, OCH, 28.37, 28.40.
    The above product was remethylated with dimethyl sulfate and




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40 per cent hydroxide solution.     A vigorous reaction took place,
and, after it had subsided, the reaction mixture was heated on the
steam bath for 20 minutes.     The product was washed with water
and dried in the Abderhalden        drier at 56” over phosphorus
pentoxide.
  Analysis-
                       (OCHJ,
                     /
              C36H3106            Calculated.   OCHI 33.29
                     \ (OCU
                                  Found.          “   32.77, 32.95
    Isolation of SecondLignin Fraction-The    straw (855 gm.) which
had been extracted exhaustively with alcoholic sodium hydroxide
solution, was treated with a sufficient 4 per cent aqueous sodium
hydroxide solution to cover it completely and heated under the
reflux condenser at 100” for 4 hours. The reaction mixture was
filtered and the lignin precipitated by the addition of concentrated
hydrochloric acid to the filtrate.    The residual straw was again
treated with a 4 per cent sodium hydroxide solution, and the
operation was repeated until the alkaline extract when acidulated
with hydrochloric acid no longer gave a precipitate of lignin. The
cellulosic residue obtained amounted to 448 gm. It still con-
tained 4.2 per cent of lignin as determined later by the fuming
hydrochloric acid method. The lignin obtained from the several
extractions was combined and purified by dissolving it in 500 cc.
of 2 per cent aqueous sodium hydroxide solution and adding to it
1 liter of 95 per cent ethanol. The precipitate was filtered off,
the filtrate was acidified with hydrochloric acid, and the alcohol
was removed by distillation.      The lignin was washed with water
until the wash water was free of chlorides and dried in vacua at 56”
                 111.Phillips and M. J. Goss                        563
over phosphorus pentoxide.     Yield, 9 gm.       An amorphous    brown
substance was obtained.
  Analysis-
 Found. C 61.8, 61.8, H 5.3, 5.4, OCH, 14.68, 14.84 (ash-free basis)

   The alkoxyl groups present in this lignin fraction were identified
as methoxyls. The method previously referred to for the identi-
fication of the alkoxyl groups was used.
   The percentage composition of a compound represented by the
                     is
formula C40H4201~ C 61.68, H 5.43. The calculated percentage




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of methoxyl in a compound of this empirical formula having three
methoxyl groups is 11.95 per cent, and on the basis of four meth-
oxyl groups it is 15.92 per cent. The lignin fraction consists
chiefly of a substance containing four methoxyl groups admixed
with some material containing fewer methoxyl groups.
   Acetylation-This     was carried out according to the method
previously referred to. The percentage of acetyl was determined
by the same method used for the analysis of the acetyl derivative
of the first lignin fraction.
  Analysis-
                       Calculated. CHs.CO 18.1
       CmHas01e(CO.CHs)r.
                       Found.        ‘I   16.68, 16.39

  Methylation with Diazomethane-O.5 gm. of lignin was added to
an ether solution containing approximately     1.8 gm. of diazo-
methane and allowed to remain at room temperature for 5 days.
The product was filtered off and dried in vacua at 56” over phos-
phorus pentoxide.
  Analysis-
                  (OCH&
                /
          Cdh0r(OH)~          Calculated. OCHS23.0
                \ (OCHA
                              Found.          “     22.32,22.50

   Distillation with 12 Per Cent Hydrochloric Acid-The distillation
of the lignin with the subsequent cohobation of the distillate was
carried out as previously described. Formaldehyde was identified
in the distillate by the dimethylcyclohexanedione method already
referred to.
   Isolation of the Residual Lignin-A  portion of the residual straw
                        Chemistry      of Lignin.   X
 (112 gm. = 25 per cent of the weight of the straw) which had been
ground fine enough to pass through an SO-mesh sieve was boiled
for 3 hours under a reflux condenser with 5 liters of distilled water
to which sufficient hydrochloric     acid had been added to neutralize
the sodium hydroxide adhering to the straw.            The straw was
filtered off and boiled again for 3 hours under a reflux condenser
with 5 liters of 2 per cent hydrochloric acid solution, again filtered
off, washed with distilled water until free of acid, and dried at
105O. Yield, 73.5 gm. = 65.6 per cent of the weight of the straw.
The dry and extracted straw was added portionwise           to 1000 cc.




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of fuming hydrochloric      acid (d 1.212 to 1.223 at 15’) which was
maintained at a temperature of +S” to +lO”.           A stream of dry
hydrochloric acid gas was passed through the reaction mixture for
2 hours.    It was then allowed to stand in an ice box (+8” to + 10”)
for 24 hours.     The reaction mixture was diluted with 10 liters of
distilled water and boiled under a reflux condenser for 1 hour.       It
was allowed to cool to room temperature and was then filtered off
and washed with distilled water until free of acid. It was dried at
105’ and a brown-colored       product was obtained.    Yield, 4.8 gm.
= 4.2 per cent of the original (112 gm.) unextracted straw.
  Analysis--(Ash-free     basis)
        Found.    C 64.7, 64.7, H 5.8, 5.8, OCH3 14.96, 14.86

  The character of the alkoxyl group present in this lignin fraction
was established by the methods previously described.
  When this lignin fraction was distilled with 12 per cent hydro-
chloric acid, some formaldehyde was obtained in the distillate.

                                   SUMMARY

   1. Three lignin fractions were isolated from oat straw by extract-
ing it successively and exhaustively, first with a 2 per cent alco-
holic sodium hydroxide solution at room temperature, then by
refluxing it with a 4 per cent aqueous sodium hydroxide solution,
and finally subjecting the residue to the action of fuming hydro-
chloric acid. The composition of the first lignin fraction agreed
with that represented by the formula &,H~sO~S. Four methoxyl
groups and four hydroxyl groups were found to be present. Of
the four hydroxyl groups, two could be methylated with diaeo-
methane, thus indicating that these are more acidic, possibly
                   M. Phillips and M. J. Goss

phenolic or enolic in character.          When fused with potassium
hydroxide,     protocatechuic     acid was obtained.     The yield was
approximately      4 per cent of the weight of the lignin.      The ana-
lytical results on the second lignin fraction are more in agreement
with that represented by the formula CK,HQZOS In this lignin
fraction, approximately       four methoxyl groups and four hydroxyl
groups were shown to be present.           Two of the hydroxyl groups
could be methylated with diazomethane.          The third lignin fraction
was found to have a higher percentage of carbon than either of the
other two lignin fractions.        The percentage of methoxyl did not




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differ from that of the other two fractions.
    2. The alkoxyl groups present in all the three lignin fractions
were proved definitely to be methoxyls.
    3. All the three fractions when distilled with 12 per cent hydro-
chloric acid afforded some formaldehyde.
    4. The lignin fractions isolated from oat straw are closely related
to the corresponding      lignin fractions isolated from barley straw.
                              BIBLIOGRAPHY

1. Phillips, M., and Goss, M. J., J. Am. Chem. Sot., 66,2707 (1934).
2. Marion, L., Canad. J. Research, 6, 521 (1932).
3. Phillips, M., J. Am. Chem. SOL, 62, 793 (1930).
4. Willstatter, R., and Uteinger, M., Ann. Chem., 382, 148 (1911).
5. Weinberger, W., Znd. and. Eng. Chem., Anal. Ed., 3, 365 (1931).
6. Mulliken, S. P., A method for the identification     of pure organic   com-
            pounds, New York, 1, 81 (1965).
7. Phillips, M., J. Am. Chem. Sot., 49, 2037 (1927).
8. Phillips, M., Znd. and. Eng. Chem., Anal. Ed., 6, 321 (1934).
9. Friedrich, A., and Pelikan, E., Biochem. Z., 239,461    (1931).

								
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