Organic chemistry in our life. Part I
Organic chemistry is most commonly and simply defined as the chemistry of carbon compounds. Compared with hydrogen and helium, carbon is not an abundant element in the universe, nor in the solar system; but it is an essential element of life. Indeed, four elements: carbon, hydrogen, nitrogen and oxygen make up most of the matter found in living organisms. Trace elements such as sulfur, phosphorous, sodium, potassium and iron, to name a few, also play an important role in the chemistry of life; but it is the unique properties of carbon that permits the immense diversity of compounds associated with life. From simple single-carbon compounds such as methane and carbon dioxide to the more complex structures found in vitamins, hormones and enzymes, and ultimately to very large macromolecules like DNA, carbon is the underlying essential structural component.
Since the birth of organic chemistry over two hundred years ago, chemists have worked to unravel the structural complexities of these compounds. Today, all the facts and principles they have learned are consolidated in our texts and journals. Industrial applications have led to the manufacture of medicinal agents (drugs), synthetic fibers, plastics, dyes, pesticides and a host of other useful materials. Clearly, organic chemistry has touched all our lives. The study of organic chemistry is both fascinating and relevant, due in large part to the widespread distribution of both natural and synthetic organic chemicals.
The names of many early and some contemporary chemists are associated with important concepts and reactions. Whenever possible their names have been linked to the MSU photo-portrait gallery assembled by professor Harold Hart.
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Cellulose
A subdivision, forming what is called a colloidal solution. The starch in it is unable to pass through a membrane of
parchment paper, whereas substances in real solution are able
slowly to diffuse through such a membrane. Neither has the
starch any effect on the freezing-point of the water containing
it. When heated to about 200 C., starch is changed into dextrin.
Very characteristic of starch is the intensely blue compound which it forms with iodine. This furnishes a very sensitive test either for starch or for free iodine. The blue colour dis
appears when sufficient heat is applied, but reappears on cool
ing.
Dextrin, C 6 H 1Q O 5, is obtained by simply heating starch to
about 200 C., or by boiling it with dilute acids. Dextrin is
used as a substitute for gum. It is not coloured blue by
iodine.
Cellulose, C 6 H 1Q O 5, is the chief constituent of the cell-
walls of plants ; wood is chiefly cellulose, while cotton-wool
and filter-paper are nearly pure cellulose. This is insoluble
in all ordinary solvents, but concentrated sulphuric acid
dissolves it, and the solution when diluted and boiled yields
first dextrin and then dextrose.
The exact chemical constitution of cellulose is matter for
future investigation. It appears, however, to contain three-
fifths of its oxygen in the form of hydroxyl groups OH, as \ve
find that by the action of acids ethereal salts of cellulose may
be prepared in which three acid groups are introduced into
the formula C 6 H 10 O 5; the real molecular formula of cellulose
is unknown, but it is more convenient to regard these ethereal
salts as derived from the doubled formula C 12 H 2Q O 10 , in which,
of course, there are six hydroxyls.
The most important of these salts are the nitrates; these
are prepared by treating cellulose (cotton-wool) with strong
nitric acid, the action being aided by the addition of concen
trated sulphuric acid. When the strongest acids are employed
the product obtained is gun-cotton, which is found to be
cellulose hexa-nitrate: = C 12 H 144( N 3)(i + 6H 2) Cellulose.