Agriculture Reference
In-Depth Information
Table 7.2
Incremental Differences in Molecular Structure Leading to Changes in Physicochemical Properties and Hazards
−
log
P
◦
Solubility in
H
2
Oat25
◦
C
(mol L
−
1
)
−
log Vapor
Pressure at
25
◦
C (atm)
Physical State
at 25
◦
C
Worker Exposure Limits
(parts per million)
Compound
Regulating Agency
Methane, CH
4
Gas
2.8
−
2.4
25
Canadian Safety
Association
Tetrachloromethane
(carbon tetra-
chloride), CCl
4
Liquid
2.2
0.8
2 short-term exposure
limit (STEL)
=
60 min
National Institute of
Occupation Health
Sciences (NIOSH)
Ethane, C
2
H
6
Gas
2.7
−
1.6
None (simple asphyxiant) Occupational Safety and
Health Administration
(OSHA)
Trichloroethane,
C
2
HCl
3
Liquid
2.0
1.0
450 (STEL-15 min)
OSHA
Benzene, C
6
H
6
Liquid
1.6
0.9
5
OSHA
Phenol, C
6
H
6
O
Liquid
0.2
3.6
10
OSHA
Toluene, C
7
H
8
Liquid
2.3
1.4
150
UK Occupational and
Environmental Safety
Services
oil-based compounds readily (and these are the ones that typically need to be
removed from clothing).
The lessons for green design are many. There are uncertainties in using sur-
rogate compounds to represent entire groups of chemicals (since a slight change
can change the molecule significantly). However, there have been substantial
advances in green chemistry and computational chemistry as tools to prevent
dangerous chemicals from reaching the marketplace and the environment be-
fore they are manufactured. Subtle differences in molecular structure can render
molecules safer while maintaining the characteristics that make them useful in
the first place, including their market value.
CARBON AND RAIN
By far most carbon-based compounds are organic, but a number of inorganic
compounds are also important. In fact, the one that is getting the most attention
for its role in climate, carbon dioxide, is an inorganic compound owing to its
carbon atom lacking a covalent bond with other carbon or hydrogen atoms. Other
important inorganic carbon compounds include the pesticides sodium cyanide
(NaCN) and potassium cyanide (KCN) and the toxic gas carbon monoxide (CO).
Inorganic compounds include inorganic acids such as carbonic acid (H
2
CO
3
)
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