5.1 | INTRODUCTION
The fundamental information that environmental engineers and scientists need con-
cerning organic chemistry differs considerably from that which the organic chemist
requires. This difference is due to the fact that chemists are concerned principally with
the synthesis of compounds, whereas environmental engineers and scientists are con-
cerned, in the main, with how the organic compounds in liquid, solid, and gaseous
wastes can be destroyed and how they react in the environment. Another major differ-
ence lies in the fact that the organic chemist is usually concerned with the product of
the reaction: the by-products of a reaction are of little interest to him or her. Since few
organic reactions give better than 85 percent yields, the amount of by-products and
unreacted raw materials that represent processing wastes is of considerable magni-
tude. In addition, many raw materials contain impurities that do not enter the desired
reaction and, of course, add to the organic load in waste streams. A classical example
is formaldehyde, which normally contains about 5 percent of methanol unless special
precautions are taken in its manufacture. Unfortunately, organic chemists have pre-
sented very little information on the nature of the by-products of reactions to aid envi-
ronmental engineers and scientists in solving industrial and hazardous waste prob-
lems. Fortunately, this is changing because of the large liabilities that companies now
face from discharge of environmental pollutants. Awards are now being given for
“green chemistry,” that is, for changing the ways chemicals are produced in order to
reduce the environmental harm they or their production cause.
The environmental engineer and scientist, like the biochemist, must have a fun-
damental knowledge of organic chemistry. It is not important for either to know a
multiplicity of ways of preparing a given organic compound and the yields to be ex-
pected from each. Rather, the important consideration is how the compounds react
in the atmosphere, in the soil, in water, and in treatment reactors, especially when
serving as a source of energy for living organisms. It is from this viewpoint that or-
ganic chemistry will be treated in this chapter, and considerations will be from the
viewpoint of classes rather than individual compounds.
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5
CHAPTER
Basic Concepts from Organic Chemistry
History
Organic chemistry deals with the compounds of carbon. The science of organic
chemistry is considered to have originated in 1685 with the publication by Lémery
1
of a chemistry book that classified substances according to their origin as mineral,
vegetable, or animal. Compounds derived from plants and animals became known
as
organic
and those derived from nonliving sources were inorganic.
Until 1828 it was believed that organic compounds could not be formed except
by living plants and animals. This was known as the
vital-force theory,
and belief in
it severely limited the development of organic chemistry. Wöhler,
2
in 1828, by acci-
dent, found that application of heat to ammonium cyanate, an inorganic compound,
caused it to change to urea, a compound considered organic in nature. This discovery
dealt a death blow to the vital-force theory, and by 1850 modern organic chemistry
became well established. Today about 13 million organic compounds are known.
3
Many of these are products of synthetic chemistry, and similar compounds are not
known in nature. Approximately 70,000 organic chemicals are in commercial use.
Elements
All organic compounds contain carbon in combination with one or more elements.
The hydrocarbons contain only carbon and hydrogen. A great many compounds
contain carbon, hydrogen, and oxygen, and they are considered to be the major ele-
ments. Minor elements in naturally occurring compounds are nitrogen, phosphorus,
and sulfur, and sometimes halogens and metals. Compounds produced by synthesis
may contain, in addition, a wide variety of other elements.
Properties
Organic compounds, in general, differ greatly from inorganic compounds in seven
respects:
1.
Organic compounds are usually combustible.
2.
Organic compounds, in general, have lower melting and boiling points.
3.
Organic compounds are usually less soluble in water.
4.
Several organic compounds may exist for a given formula. This is known as
isomerism.
5.
Reactions of organic compounds are usually molecular rather than ionic. As a
result, they are often quite slow.
6.
The molecular weights of organic compounds may be very high, often well
over 1000.
7.
Most organic compounds can serve as a source of food for bacteria.
CHAPTER
5
Basic Concepts from Organic Chemistry
213
1
Nicholas Lémery (1645–1715), French physician and chemist.
2
Freidrich Wöhler (1800–1882), German chemist.
3
R. Chang, “Chemistry,” 7th ed., McGraw-Hill, New York, 2002.
214
PART
1
Fundamentals of Chemistry for Environmental Engineering and Science
Sources
Organic compounds are derived from three sources:
1.
Nature:
fibers, vegetable oils, animal oils and fats, alkaloids, cellulose, starch,
sugars, and so on.
2.
Synthesis:
A wide variety of compounds and materials prepared by
manufacturing processes.
3.
Fermentation:
Alcohols, acetone, glycerol, antibiotics, acids, and the like are
derived by the action of microorganisms upon organic matter.
The wastes produced in the processing of natural organic materials and from the
synthetic organic and fermentation industries constitute a major part of the indus-
trial and hazardous waste problems that environmental engineers and scientists are
called upon to solve.
The Carbon Atom
A question commonly asked is: How is it possible to have so many compounds of car-
bon? There are two reasons. In the first place, carbon normally has four covalent bonds
(four electrons to share). This factor alone allows many possibilities, but the most im-
portant reason is concerned with the ability of carbon atoms to link together by cova-
lent bonding in a wide variety of ways They may be in a continuous open chain,
or a chain with branches,
or in a ring,
or in chains or rings containing other elements,
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