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‫جامعة الســــــويــــــــــــس‬
E1 AND E2 MECHANISM, CHEMICAL
COMPOSITION AND PROPERTIES OF PETROLEUM.
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Abstract
This document presents the research about E1 and E2 mechanism, chemical
compositions and properties of petroleum, it begins with E1 and E2 mechanism where
it discuses mainly kinetics, order of reactivity of alkyl halides and comparison between
E1 and E2 reactions, Ozonolysis, of alkenes, Markownikoff’s orientation. Finally, its
details the chemical composition and properties of petroleum, which is mainly,
constitute of different types of hydrocarbons which consist of carbon and hydrogen,
some of which also contain heteroatoms mostly sulfur, oxygen and nitrogen. They
main hydrocarbon types explained in this paper include paraffin’s, naphthene
(cycloparaffins), aromatics, and hydrocarbons series. It also covers the chemical
composition and physical properties of petroleum. The contents used in this paper are
data collection analysis.
1- Introduction
The elimination reaction in a different types of organic reaction in which two
substituent’s are removed from a molecule in one or two step mechanism where it
describe the reaction that goes by second-order kinetics, Hughes and ingold is
referred as E2 mechanism of reaction and it is one-step mechanism and the two-step
mechanism is known as E1 reaction. It also covers the comparative differences
between E2 bimolecular and the goes in second order while E1 is unimolecular first
order. The composition of petroleum is a complex mixture that constitute primarily of
hydrocarbons, derived from ancient living organisms deposited as geological
sediments.
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2- Literature Review
Elimination reaction is a type of organic reaction in which two substituents are
removed from a molecule in either a one or two- step mechanism. The one –step
mechanism is known as the E2 reaction and the two-step mechanism is known as the
E1 reaction. In most organic elimination reactions, at least one hydrogen is lost to
form the double bound. The unsaturation of the molecule increases. It is also possible
that a molecule undergoes reductive elimination, by which the valence of an atom in
the molecule decreases by two, though this is more common in inorganic chemistry.
There are three importance events in these elimination reactions:
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i.
Removal of a proton
ii.
Formation of the CC
iii.
Breaking of the bond to the leaving
bond.
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CHARACTERISTIC OF E1 AND E2 MECHANISM
Characteristics of E1 reaction
Characteristics of E2
Unimolecular reaction
Biomolecular reaction
Two step reaction
Single step reaction.
Carbocation intermediate formed. Hydrogen removes from beta
carbon.
Reactivity order of RX is
3
4
2
1
Trans elimination because low
energy consumption
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No stereospecific
Anti-periplanar attack
Follow Zaitsev rule.
Polar aprotic solvent best.
Polar protic solvent good
Phenyl group influences
because stabilized ionic
elimination because product
intermediate
alkenes further stabilized by
resonance.
Rate of reaction increases when
Reactivity order 3
concentration of substrate
steric effect.
2
1 . No
increases
Rearrangement may take place.
Strong nucleophile influence
elimination.
No intermediate formed.
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Examples.
e
A. E1 MECHANISM.
• E1 indicates an elimination, Unimolecular reaction, where rate = K R-LG . (R-LG = Substrate)
H⎯C⎯C⎯LG→ H⎯C⎯C
LG
Loss of the leaving group, LG, to generate a carbocation intermediate then.
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B
H⎯C⎯C+
B⎯H
C=C
Loss of proton H +, from the carbocation to form the
-bond
Reaction influence the reaction pathway:
E1 mechanistic pathway is most common with:
Good leaving groups
Stable carbocation Weak bases.
E1 reaction is non-stereo specific follows Zaitsev rule
Does not occur with primary alkyl halides (leaving groups).
E1 mechanism for Alcohols.
H+
H⎯C⎯C⎯OH
C= C
E1 Mechanism for Alkyl Halides.
−
B
H⎯C⎯C⎯X
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C=C
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X= I, Br, C1, (F)
B. E2 MECHANISM.
E2 Mechanism indicates an elimination, biomolecular reaction where rate = K (B) [RLG]. This implies that the rate-determining step involves an interaction between these
two species, the base B, and the organic substrate, R-LG.
• Kinetics---- second order
• Mechanism-single step.
• Stereospecific
• Concerted-all bonds form and break at same time
• Favored by strong base.
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C.
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OZONOLYSIS
Ozonolysis is an organic reaction where the unsaturated bonds of alkenes, alkynes, or
azon compounds are cleaved with ozone.
D.
MARKOWIKOFF; S RULE:
The rule state that with addiction of a protic acid HX to asymmetric alkenes, the acid
hydrogen (H) becomes attached to the carbon with more hydrogen substituents, and
the halide (X) group becomes attached to carbon with more alkyl substituents.
CHEMICAL COMPOSITION AND PROPERTIES OF
PETROLEUM.
Composition by weight element percent range as
follow, carbon 83 to 85%, hydrogen 10 to 14% nitrogen 0.1 to 2% Oxygen 0.05 to
1.5% sulfur 0.05 to 6.0% metals 0.1%
Hydrocarbon average range Alkenes (paraffins) 30% 15 to
60% Naphthene 49% 30 to 60% Aromatics 15, 3 to30%
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Asphaltic 6% remainder. Lighter hydrocarbons methane, ethane, propane and butane
occur as gases pentane and heavier ones are in the form of liquids or solids.
A. Hydrocarbon series.
A saturated hydrocarbon (some time called alkane) is one which the valence of all the
carbon atoms is satisfied by single bonds for each carbon atom is connected to each
other carbon atom by a single covalent bond e.g. paraffins. A saturated hydrocarbon
is one in which the valence of some of the carbon atom is not satisfied by single bond,
so that these atoms are connected to one another with two or more covalent bonds
e.g. benzene.
Paraffin
Paraffins are also known as Alkanes and have the general formula of CnH2n+2 where
n is the number of carbon atoms. Paraffins from C1 to C40 usually appear in crude oil
and represent up to 20% crude by volume. They are stable and remain unchanged
over long periods of geological time.
Naphthene.
Naphthene or cycloparaffins are ring or cyclic saturated hydrocarbons with the general
formula CnH2n. thermodynamic studies show that naphthene rings with five and six
carbon atoms are the most stable naphthenic hydrocarbons. The content of
cycloparaffins in petroleum may vary up to 60%.
Aromatics.
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Aromatics are an importance series of hydrocarbons found in most every petroleum
mixture from any part of the world. This series of aromatics is called alkyl benzenes
and have a general formula of CnH2n-6 (where n 6).
Asphaltenes
They are composed of fused benzene-ring network, but they contain impurity atoms
and are not true hydrocarbons. These impurities are the high in molecular weight
compound previously referred to as NSO compounds. Asphaltenes are heavy
compound of crude oil and the major components in many natural tars and asphalts.
CHEMICAL PROPERTIES OF PETROLEUM.
Hydrocarbons are found in nature in many different forms, mainly as: Liquid
petroleum: known as crude oil to distinguish it from refined oil it is most important
commercially.
Natural gas: which is lighter fraction of hydrocarbons, can be free or dissolved.
Asphalt, tar, and pitch:
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CHEMICAL COMPOSITION OF TYPICAL PETROLEUM.
ELEMENT
NATURAL
CRUDE
GAS
OIL
65-80
82-87
80-85
HYDROGEN 1-25
12-15
9-11
SULPURE
0.2
0.1-6
2-8
NITROGEN
1-15
0.1-2
0-2
OXYGEN
0
5-0.1
0
CARBON
ASPHALT
Physical properties of petroleum.
The physical properties are most commonly used in petroleum are as follows.
Specific gravity, volume, viscosity, refraction index, fluorescence, optical activity,
color, odor, boiling point.
3- Research Goal
To understand E1 AND E2 reactions and how the differ significantly in the nature of
transition states that determine the Regio chemistry of the product, the pathway
involves a transition state leading from starting material directly to the product, to
understand two main methods involved in the reaction that is dehydration (elimination
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of water) and dehydrohalogenation (Removal of a hydrogen atom and a halogen
atom).
To know the petroleum properties and how they are use in to check quality of fuel oil,
to differentiate between difference of petroleum using chemical or physical properties.
4- Results and Discussion
Because there are two mechanisms for nucleophilic substitution, there are also two
elimination mechanisms. The E1 mechanism is nearly identical to the Sn1
mechanism, differing only in the course of reaction. The alkanes from Pentane
(C5H12) to Octane (C8H18) are refined into petrol and the one from nonane (C9H20)
to hexadecane (C16 H34) are refined into diesel fuel, kerosene and jetfoil. Alkanes
with more than 16 carbon atoms can be refined into fuel oil and lubricating oil.
Paraffins wax is an alkane with approximately 25 carbon atoms. Asphalt has 35 and
up carbon atoms. Those with four or fewer carbon atoms are in gaseous state at room
temperature.
5- Conclusion
The usual mechanism for dehydrohalogenation is E2 mechanism.
It exhibits second order kinetics, and both the alkyl halide and the base appear in the rate
equation. The reaction is concerted- bonds are broken and form single step. Regarding
chemical composition and properties of petroleum, the hydrocarbon structures found in oil
include saturates, aromatics, and polar compounds that include resins and asphaltenes.
The resins and asphaltenes are largely recalcitrant in the environment.
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6-References
Robert J. Ouellette, j. David rawn, in organic chemistry, Haloalkanes and alcohols
nucleophilic substitution and elimination reaction, second edition, 2018.
Chemicals composition of petroleum journal, by Chang Samuel Hsu, Paul R Robinsin.
https://www.link.spriger.com
https://www.sciencediret.com, origin, composition and properties of petroleum.
https://www.slideshare.net physical and chemical properties of petroleum Oct 8, 2016.
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