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The Chemistry and Technology of Petroleum
such as 3-methylheptane [CH 3 CH 2 CH(CH 3 )CH 2 CH 2 CH 2 CH 3 ], interfere with adduct formation, presumably because the dimensions of the molecules at the methyl group are too great to allow the
hydrocarbons to fit properly into the urea adduct channel. However, in the presence of an adducting
n-paraffin, such as n-decane, the methyl-substituted paraffins are assisted into the adduct (induction). 3-Methyleicosane [CH 3 CH 2 CH(CH 3 )CH 2 (CH 2 ) 15 CH 3 ], presumably because of its sufficiently
long unbranched chain, forms adducts readily.
When the carbon chain is sufficiently long, ring structures do not prevent adduct formation. For
example, 1-phenyloctadecane [C 6 H 5 CH 2 (CH 2 ) 16 CH 3 ] forms an adduct with urea but 1-phenyloctane
[C 6 H 5 CH 2 (CH 2 ) 6 CH 3 ] does not participate in adduct formation. The stability of the adduct formed
from the phenyl-paraffins or cyclohexyl-paraffins is usually considerably less than those of the corresponding straight-chain hydrocarbons having the same number of carbon atoms.
Many classes of organic compounds form adducts, and some examples of these are ketones,
acids, esters, halides, mercaptans, and ethers; both saturated and unsaturated structures adduct,
provided the chain is sufficiently long. The carbonyl oxygen in ketones, acids, and esters does not
appear to interfere with adduct formation and, to some extent, even aids the process since shorter
carbon chains are adducted in oxygenated compounds. Thus, acetone, with a straight chain of three
carbon atoms, n-butyric acid with four carbon atoms, and their higher homologues form complexes
with urea. Among the alkyl halides, 1-bromohexane, but not 2-bromohexane, forms an adduct;
2-bromodecane can be adducted, indicating that an unsubstituted chain of eight carbon atoms is
sufficient to overcome substituent effects.
9.5.2.2 Thiourea Adduction
The relationship among structure, adductability, and adduct stability is not as well defined for the
thiourea-adductible compounds as for the urea-reactive hydrocarbons. The stability of any thiourea
adduct is quite low, even at 0°C, and corresponds approximately to the stability of the urea completes
of the lower n-paraffins. The high stability of the urea completes of the higher n-paraffins has no parallel in thiourea completes. Among the higher hydrocarbons containing a ring or branching and a long
chain there is a lesser tendency for the thiourea adducts to form than in the lower molecular weight
homologues, as the alkyl chain apparently reduces the stability. The higher n-paraffins adduct fairly
readily and become more stable with increasing molecular weight, but the stability of these adducts is
still of the same low order of magnitude as the lower molecular weight iso-paraffins and naphthenes.
9.5.2.3 Adduct Composition
Analysis of the complexes for the ratio of reagent to reactant may be made by several methods. The
urea (or thiourea) content of the crystalline complex may be established by nitrogen determination,
or the amount of organic component may be determined from carbon content or by the weight loss
upon dissociation of the adduct. Also, measurement of concentration changes in the reaction liquid
is applicable to certain mixtures.
For urea adducts of normal hydrocarbons, the mol ratio of urea to hydrocarbon in the adduct can
be represented by the equation
m
n
=
+
0.
.
65 1 5
where
m is the mol ratio of urea to hydrocarbon
n is the number of carbon atoms in the hydrocarbon
For all practical purposes, the use of the ratio of 3.3 g of urea per gram of normal hydrocarbon is
more convenient. The greater variety of hydrocarbon structures adducting with thiourea than with
urea adversely affects development of an equation relating the mol ratio of thiourea to reactant. For
a given number of carbon atoms, the more compact molecules are generally associated with less
The Chemistry and Technology of Petroleum
such as 3-methylheptane [CH 3 CH 2 CH(CH 3 )CH 2 CH 2 CH 2 CH 3 ], interfere with adduct formation, presumably because the dimensions of the molecules at the methyl group are too great to allow the
hydrocarbons to fit properly into the urea adduct channel. However, in the presence of an adducting
n-paraffin, such as n-decane, the methyl-substituted paraffins are assisted into the adduct (induction). 3-Methyleicosane [CH 3 CH 2 CH(CH 3 )CH 2 (CH 2 ) 15 CH 3 ], presumably because of its sufficiently
long unbranched chain, forms adducts readily.
When the carbon chain is sufficiently long, ring structures do not prevent adduct formation. For
example, 1-phenyloctadecane [C 6 H 5 CH 2 (CH 2 ) 16 CH 3 ] forms an adduct with urea but 1-phenyloctane
[C 6 H 5 CH 2 (CH 2 ) 6 CH 3 ] does not participate in adduct formation. The stability of the adduct formed
from the phenyl-paraffins or cyclohexyl-paraffins is usually considerably less than those of the corresponding straight-chain hydrocarbons having the same number of carbon atoms.
Many classes of organic compounds form adducts, and some examples of these are ketones,
acids, esters, halides, mercaptans, and ethers; both saturated and unsaturated structures adduct,
provided the chain is sufficiently long. The carbonyl oxygen in ketones, acids, and esters does not
appear to interfere with adduct formation and, to some extent, even aids the process since shorter
carbon chains are adducted in oxygenated compounds. Thus, acetone, with a straight chain of three
carbon atoms, n-butyric acid with four carbon atoms, and their higher homologues form complexes
with urea. Among the alkyl halides, 1-bromohexane, but not 2-bromohexane, forms an adduct;
2-bromodecane can be adducted, indicating that an unsubstituted chain of eight carbon atoms is
sufficient to overcome substituent effects.
9.5.2.2 Thiourea Adduction
The relationship among structure, adductability, and adduct stability is not as well defined for the
thiourea-adductible compounds as for the urea-reactive hydrocarbons. The stability of any thiourea
adduct is quite low, even at 0°C, and corresponds approximately to the stability of the urea completes
of the lower n-paraffins. The high stability of the urea completes of the higher n-paraffins has no parallel in thiourea completes. Among the higher hydrocarbons containing a ring or branching and a long
chain there is a lesser tendency for the thiourea adducts to form than in the lower molecular weight
homologues, as the alkyl chain apparently reduces the stability. The higher n-paraffins adduct fairly
readily and become more stable with increasing molecular weight, but the stability of these adducts is
still of the same low order of magnitude as the lower molecular weight iso-paraffins and naphthenes.
9.5.2.3 Adduct Composition
Analysis of the complexes for the ratio of reagent to reactant may be made by several methods. The
urea (or thiourea) content of the crystalline complex may be established by nitrogen determination,
or the amount of organic component may be determined from carbon content or by the weight loss
upon dissociation of the adduct. Also, measurement of concentration changes in the reaction liquid
is applicable to certain mixtures.
For urea adducts of normal hydrocarbons, the mol ratio of urea to hydrocarbon in the adduct can
be represented by the equation
m
n
=
+
0.
.
65 1 5
where
m is the mol ratio of urea to hydrocarbon
n is the number of carbon atoms in the hydrocarbon
For all practical purposes, the use of the ratio of 3.3 g of urea per gram of normal hydrocarbon is
more convenient. The greater variety of hydrocarbon structures adducting with thiourea than with
urea adversely affects development of an equation relating the mol ratio of thiourea to reactant. For
a given number of carbon atoms, the more compact molecules are generally associated with less