
pHairway?/span> vs. N-Control
?/span>vs.Sulfuric Acid
1.The monourea adduct of sulfuric acid is by far the most
active combination of urea and sulfuric acid for use in this invention. The diurea
sulfuric acid adduct exhibits little if any ability to modify cellulose either chemically
or physically. Although uncomplexed sulfuric acid rapidly attacks cellulosic materials, it
does so primarily by oxidation and sulfonation, and in doing so, it is consumed by
conversion to sulfates and similar reaction products. The reaction of sulfuric acid and
cellulosic materials also results in the destruction of the cellulosic material.
Accordingly, the most preferred compositions are those in which essentially all of the
urea and sulfuric acid are present as the monoureasulfuric acid adduct. Such compositions
have a urea/sulfuric acid molar ratio of 1/1. Compositions containing substantial amounts
of either the diurea adduct or free sulfuric acid can be employed although they are not as
active as the compositions having urea/sulfuric acid molar ratios of 1/1 in the methods of
this invention. Thus, the preferred solid and aqueous urea-sulfuric acid components are
those in which at least about 75, usually at least about 85, and most preferably at least
about 90 percent of the sulfuric acid is present as the mono-and/or diurea-sulfuric acid
adduct. Particularly preferred compositions are those that contain essentially no free
sulfuric acid; thus, essentially 100 percent of the sulfuric acid would be combined with
urea as the mono- and/or diurea adduct. Furthermore, since the monourea adduct is the most
active combined form of urea and sulfuric acid, at least about 25, usually at least about
50, preferably at least about 70, and most preferably about 80 to about 100 percent of the
sulfuric acid is present as the monourea-sulfuric acid adduct.
2. Although the monourea adduct appears to dissociate to urea and sulfuric acid in
solutions containing significantly less than about 0.5 weight percent combined urea and
sulfuric acid, the dissociated components will recombine to form the active adduct on the
treated cellulosic material upon evaporation of water from the solution.
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3. Other components that do not substantially negate the
proton-donating activity of the mono-adduct of sulfuric acid may also be present
4.. Substantial amounts of uncomplexed sulfuric acid, i.e.,
sulfuric acid that is not complexed with a chalcogen compound as either the mono-or
di-adduct, are less preferred since sulfuric acid, when present in substantial amounts,
may promote side reactions such as oxidation, sulfonation, dehydration and/or other
reactions. While the di-adduct is generally not detrimental to the performance of the
mono-adduct components as acid catalysts for organic reactions, it has little or no
proton-donating ability and thus little or no activity as a catalyst for acid-catalyzed
organic reactions.
5. I have found that the monourea adduct of sulfuric acid efficiently and rapidly
hydrolyzes polysaccharides in the presence of water. The monourea adduct is not present
when the urea/sulfuric acid molar ratio is 2 or more. In such compositions all of the
sulfuric acid is present as the diurea adduct. The diurea adduct of sulfuric acid has
little or no polysaccharides-hydrolyzing activity.
6. Furthermore, the
attenuation of strong acid proton lability increases as the extent of adducting is
increased in the case of acids, such as sulfuric acid, which will combine with more than
one mole of chalcogen compound per mole of acid. Thus, the protonic acidity of sulfuric
acid decreases as the chalcogen compound/acid molar ratio is increased from 1 to 2.
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