Chemistry Reference
In-Depth Information
reserves the term ''synthetic'' for the more modern products of chemical techno-
logy, primarily petroleum-derived, that have been developed in the twentieth century
and generally show important improvements over the older soap technology. The
chemical processes required for the production of modern surfactants and deter-
gents are also usually much more complicated than the simple neutralization
involved in soap manufacture. In this context, the term ''simple'' is relative, as is
well known to anyone who has ever tried to prepare homemade soap.
2.2.3.2. Saturated Hydrocarbons or Paraffins
The hydrophobic groups derived from petroleum are principally hydrocarbons,
originating from the paraffinic or higher-boiling fractions of crude oil distillates.
The chain lengths most suitable for surfactant hydrophobes, C
10
-C
20
, occur in
the crude oil cuts boiling somewhat higher than gasoline, namely, kerosene and
above. The main components of kerosene are saturated hydrocarbons ranging
from C
10
H
22
to C
15
H
32
, ordinarily containing 10-25% of straight-chain homologs.
There may be significant amounts of branched-chain isomers present, in addition to
quantities of saturated cyclic derivatives, alkyl benzenes, and naphthalenes, and
minor amounts of other polycyclic aromatics.
The paraffins have the disadvantage of being relatively chemically unreactive so
that direct conversion to surfactants is difficult. As discussed above, substitution of
one or more hydrogen atoms with halogen offers a pathway to some surfactant sys-
tems, but manufacturing complications can be an impediment. It is usually neces-
sary to synthesize the surfactant by way of some more reactive intermediate
structures, commonly olefins, alkyl benzenes, or alcohols. Such compounds contain
reactive sites that are more easily linked to the required solubilizing groups.
2.2.3.3. Olefins
Olefins with the desired chain length are prepared by building up molecules from
smaller olefins (oligomerization), by breaking down (cracking) larger molecules, or
by direct chemical modification of paraffins of the desired chain length. An impor-
tant historic example of surfactant-grade olefin production by the oligomerization
process is the preparation of tetrapropylene, C
12
H
24
:
CH
CH
3
CH
2
!ð
mixed isomers of C
12
H
24
olefins and higher and lower
homologs
Þ
This may be prepared by the oligomerization of propylene, a byproduct of refinery
operations, under the influence of a phosphoric acid catalyst. The reaction condi-
tions are drastic, and extensive random reorganization of the product molecules
occurs with substantial formation of intermediate isomers in the C
10
-C
14
range.
The final product is composed of a variety of highly branched isomers and homo-
logs, with the double bond usually situated internally in the molecule.
A second type of built-up olefin is that obtained by the polymerization of ethy-
lene using a Ziegler-Natta catalyst. Such materials are predominantly linear with
even carbon numbers, although branched isomers are present in small amounts. The
