Lyons W.C. (ed.). Standard handbook of petroleum and natural gas engineering.2001- Volume 1

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Chemistry

305

[

nC,H,, (n-pentane)]

[

(

CH,),CHC,H, [(CH,),C

(neopentane)]

(isopentane)]

while

C,,H,,

(decane) has

75,

and

C,,H,

(eicosane) has

366,319

possible isomers.

Whereas n-alkanes exhibit smooth and graded variations in physical properties

(see Table

2-41),

the branched members do not

[49,

861.

The structural isomers of

any alkane generally show dissimilar physical and chemical characteristics.

branched-

chain isomer has a lower boiling point than a straight-chain isomer, and the more

numerous the branches, the lower its boiling point. Alkanes are either nonpolar or

weakly polar. They are soluble in nonpolar or weakly polar solvents (e.g., benzene,

chloroform, ether), and are insoluble in water and other highly polar solvents. Alkanes

can dissolve compounds

low polarity. Chemically, paraffins are stable and quite

unreactive at ordinary conditions. At high temperatures, they can burn completely in

the presence of excess oxygen

air to yield

CO,

and

H,O

as products. The combustion

reaction is exothermic.

At ambient temperature and pressure, the first four members of the n-alkane series

(methane to n-butane) are gases, the next thirteen (n-pentane through n-heptadecane)

are liquids, and the higher members from n

18 on are solids.

Alkenes.

These are also called "olefins" and have the general formula

CnHPn,

with n

They contain a single

C=C

double bond and are named in accordance

with the

IUPAC

convention by specifying the location

the double bond from the

terminal carbon atom nearest to it.

The first three members of the olefin series are ethylene, propylene, and butylene

(or

butene). Structural isomers exist when n

as a consequence of the positioning

of the double bond in normal alkenes

a result of branching in branched alkenes.

In addition,

geometric

isomers

may be possible owing to restricted rotation

atoms

about the

C=C

bond. For instance,

C,H,

(butene) has four possible isomers instead

of the expected three:

[CH,CHCH,CH, [CH,CHCHCH, [(CH,),CCH,

(1-butene)] (2-butene)] (isobutene)]

This occurs because 2-butene, itself, can exist in two different structures, the cis-

or the trans- configurations, depending on whether the methyl groups are situated

on the same side or on opposite sides of the main chain.

306

General Engineering and Science

Table

2-41

Physical Properties

Normal Alkanes

[47]

Melting Boiling

State Under

Molecular Point

Point

Gr Atmospheric

Name Formula

(“C)

(liquid) Conditions

Methane

Ethane

Propane

n-Butane

n-Pentane

n-Hexane

n-Heptane

n-Octane

n-Nonane

n-Decane

n-Undecane

n-Dodecane

n-Tridecane

n-Tetradecane

n-Pentadecane

n-Hexadecane

n-Heptadecane

n-Octadecane

n-Nonadecane

n-Eicosane

n-Heneicosane

n-Docosane

n-Tricosane

n-Tetracosane

n-Pentacosane

n-Triacontane

n-Pentatriacontane

n-Tetracontane

n-Pentacontane

n-Hexacontane

n-Dohexacontane

n-Tetrahexacontane

n-Heptacontane

-1

-187

-1

-95

-9

-57

-54

-30

-26

-1

-6

104

101

102

105

-1

-89

126

151

174

196

21 6

235

254

271

287

302

31 6

330

343

356

369

380

391

402

450

490

525

0.4240

0.5462

0.5824

0.5788

0.6264

0.6594

0.6837

0.702

0.7179

0.7298

0.7404

0.7493

0.7568

0.7636

0.7688

0.7749

0.7767

0.7776

0.7777

0.7782

0.7778

0.7797

0.7786

0.7979

0.8064

0.81 26

0.81 72

0.7940

Gas

Liquid

Solid

CH3 CHs CHJ H

and

c=c

C=C

H CHs

(cis-2-butene) (trans-2-butene)

With the inclusion

these

two

geometric isomers, butene has a total of four isomers.

Chemistry

307

Alkenes also form a homologous series; as the carbon number increases, the number

possible isomeric structures for each member increases more rapidly than in the

case of the alkane series.

The physical properties of alkenes [49,

1521

are not very different from the

corresponding members

the alkane family. Alkenes are nonpolar or at most weakly

polar. They are insoluble in water but are soluble in concentrated

H,SO,

and liquid

HF.

Analogous to n-alkanes, normal alkenes dissolve in nonpolar or weakly polar

organic liquids such as ethers, CCl,, and hydrocarbons. In general, the cis- isomer

has a slightly higher polarity, a higher boiling point, and a lower melting point than

the trans- isomer, but there are exceptions. Chemically, olefins are more reactive

than paraffins due to the presence of the double bond, which can be split into two

single (stable) bonds.

Alkadienes, alkatrienes, and alkatetraenes (poly-enes).

These are unsaturated

aliphatic hydrocarbons containing two, three, or four

C=C

double bonds, respectively.

Alkadienes are also called “diolefins” or “dienes,” and alkatrienes are also known as

“triolefins” or “trienes.” Alkenes containing multiple double bonds fall under the

general class of “poly-enes.” Double bonds that alternate with single bonds in a straight

chain are said to be

conjugated.

Examples are

CH,= CH

CH CH,

(1,3-butadiene)

CH,

Double bonds that occur together in a straight chain are said to be

cumulated.

(1,3,5-hexatriene)

Examples are

CH,

the double bonds are separated by more than one single bond, they are said to

[allene (propadiene)]

(2,3-pentadiene)

isolated

unconjugated.

An example is

CH,

Although alkadienes have a higher degree

unsaturation than alkenes, their

chemical behavior is similar to alkenes, and their physical properties are similar to

alkanes containing the same number of carbon atoms. Common

alkenyl

groups include

(1,4-pentadiene)

CH,,

CH,

CHCH,

CH,CH

CHCH,

(vinyl) (allyl) (propenyl) (crotyl)

Alkynes.

These contain

single triple bond and have the general formula

CnHyn-,,

with n

Alkynes are also referred to as “acetylinic compounds.” The simple alkynes

are alternatively named as derivatives of acetylene, e.g.,

HC-

[acetylene (or ethyne)]

CH,C

(methylacetylene or propyne)

Rutyne,

C,,H,;,

exists as two isomers:

CH,CH,C

CII

CH,C

CH,4

(1-butyne or ethylacetylene)

(2-butyne or dimethylacetylene)

308

General Engineering and Science

Physical properties of alkynes

[49,

2511 are essentially similar to those

alkanes and alkenes. These compounds are weakly polar and are insoluble in water,

but they are quite soluble in organic solvents

low polarity (e.g., ether, benzene,

CCl,). Chemically, alkynes are more reactive than alkanes but behave like alkenes.

The triple bond appears to be less reactive than the double bond in some reagents

while more reactive in others. In a chemical reaction, the triple bond is usually broken

into a double bond, which may eventually split into single bonds.

Diynes and triynes refer to alkynes containing two

three triple bonds;

polyynes

contain multiple triple bonds. A conjugated triyne is a straight-chain hydrocarbon

with triple bonds alternating with single bonds. An examples is

CH,

When both double and triple bonds occur in the same molecule, the IUPAC system

recommends the use of both endings -ene, and -yne, with the former always preceding

the latter in the name. Common

alkynyl

groups are

CH,

(2,4,6-octatriyne)

HCGC- and HC=C-CH,-

(ethynyl) (P‘OPargYU

Cyclic

Hydrocarbons.

These are structures in which the carbon atoms form a ring

instead

an open chain. They are also called “carbocyclic” or “homocyclic”

compounds. They are divided into two classes: alicyclic

(or

cycloaliphatic) and aro-

matic compounds.

AIkydk

HydfoCafbOnS.

These refer to cyclic analogues of aliphatic hydrocarbons

and are named accordingly, using the prefix “cyclo-.” Their properties are similar to

their open-chain aliphatic counterparts. Alicyclic hydrocarbons are subdivided into

monocyclic (cycloalkanes, cycloalkenes, cycloalkynes, cycloalkadienes, etc.) and poly-

cyclic aliphatic compounds. Monocyclic aliphatic structures having more than

carbon atoms in the ring are known, but those containing

carbon atoms are

more commonly found in nature

[47,

p. 281.

Cycloalkanes

(or

naphthenes).

These are also known as “cycloparaffins

“saturated

alicyclic hydrocarbons.” They are quite stable compounds with the general formula

C,Hsn, with n

for rings without substituent groups. The first two members are

(cyclopropane)

H2C

CH2

CHz

CH2

(cyclobutane)

CHz

the next two being cyclopentane

and cyclohexane

For

convenience, aliphatic

rings are represented by polygons.

When substituent groups are present, they are identified and their positions

indicated by numbers in naming the compound.

an example, dimethylcyclohexane

has three structures:

Chemistry

309

b""

CHs

(

1,2-dirnethylcyclohexane)

(1,3-dimethylcyclohexane)

(

1,4-dimethylcyclohexane)

Cis-trans isomerism occurs in each of the above disubstituted cycloalkanes.

Physical properties of cycloalkanes

[49,

284;

50,

311

show reasonably gradual

changes, but unlike most homologous series, different members exhibit different

degrees of chemical reactivity. For example, cyclohexane is the least reactive member

in this family, whereas both cyclopropane and cyclobutane are more reactive than

cyclopentane. Thus, hydrocarbons containing cyclopentane and cyclohexane rings

are quite abundant in nature.

Cycloalkenes

and

cyclohexadienes.

These unsaturated cyclic aliphatic compounds

[49,

p. 2841 have one and two double bonds, respectively, in the ring. Examples are

CH2 CH

(1-cyclopentene)

CH2 CH

/\2

(1,4-~yclohexadiene)

CH CH2

They are chemically as reactive as their straight-chain counterparts. Cycloalkenes can

lose their double bond in addition reactions. In scission or cleavage reactions, the

ring structure opens up into a straight chain.

Hydrocarbons containing both aliphatic and alicyclic parts may be named by con-

sidering either part as the parent structure and the other part as a substituent, e.g.,

CHz

(ethylcyclopropane)

CH2 -CHJ

CH2

Cycloalkynes.

These structures have one triple bond in the carbon ring, as shown in

the following example:

310

General Engineering and Science

Although it is possible to conceive of alicyclic hydrocarbons containing more than

a triple bond or two double bonds in the carbocyclic ring, such ring structures are

usually either unstable or have transient existence.

Polycyclic aliphatic hydrocarbons.

These may contain two or more rings that share

two or more carbon atoms. An example of a fused-ring system is

[decahydronaphthalene (or decalin)]

The aliphatic rings may be saturated or partially unsaturated. Spiro hydrocarbons

also

belong to the polycyclic group. More examples may be found in the

CRC

Handbook

[63].

Aromatic Hydrocafbons

(Of

Arenes).

These are unsaturated cyclic compounds,

usually with benzene or its derivatives as the common building block. Their chemical

reactivity is similar to benzene. Benzene, the simplest aromatic hydrocarbon, has the

molecular formula C,H,. It is a flat and symmetrical molecule with six carbon atoms

arranged in a hexagonal ring (bond angle

120") with six attached hydrogen atoms.

The resonance theory has been proposed to explain the high thermochemical stability

of benzene. According to this theory, the benzene ring has six identical hybrid bonds

between the carbon atoms, each one intermediate between a single and a double

bond. It postulates that the molecule has a hybrid structure between the following

two resonance configurations:

and is represented by

It is important to note that benzene does not behave like a typical cyclic olefin in

that the benzene ring undergoes ionic substitution rather than addition reactions;

the ring also resists hydrogenation and is chemically more inert. Despite this, it is

still a common practice to represent benzene with three double bonds as if it

were 2,4,6-~yclohexatriene.

It is convenient to divide aromatic hydrocarbons into two groups:

(1)

benzene

derivatives, and (2) polynuclear aromatics containing multiring structures.

Benzene derivatives.

The nomenclature is a combination of the IUPAC system and

traditional names.

Many

of the derivatives are named by the substituent group appearing

as the prefix. These may be considered a subclass of the aliphatic-aromatic hydrocarbon

family, which contains both aliphatic and aromatic units in its structures. Thus,

alkylbenzenes are made up

a benzene ring and alkane units; alkenylbenzenes are

composed of a benzene ring and alkene units; and alkynylbenzenes comprise a ben-

zene ring and alkyne units. Examples of alkylbenzenes include

or C,H,CH, [toluene (or methylbenzene)]

Chemistry

311

several groups are attached to the benzene ring, their names as well as their

relative positions should be indicated.

For

example, dimethylbenzene or xylene,

C H

(CH,),,

has three geometric isomers, with prefixes ortho-, meta-, and para-,

iididating the relative positions

the

two

methyl groups.

CHs

[ortho-xylene (o-xylene or

[meta-xylene (m-xylene or [para-xylene (p-xylene

1,2-dimethylbenzene)]

1,3dimethylbenzene)] 1,4-dimethylbenzene)l

Examples

an alkenylbenzene and an alkynylbenzene are given below:

CH2 CECH

[styrene (phenylacetylene)

(vinylbenzene)]

When the benzene ring is regarded as the substituent group,

is called phenyl

group and is represented by

An example

CH2

CH2 or

CH,CHCH,(C,H,)

(3-phenylpropene)

Polynuclear aromatic hydrocarbons.

These consist

a variety

complex structures

made up of aromatic rings alone, or combinations

aliphatic rings, aromatic rings,

and aliphatic chains, etc. One such class of compounds is biphenyl and its derivatives,

in which

two

benzene rings are connected by a single C

C linkage. The structural

formula of biphenyl (or phenylbenzene) is

312

General Engineering and Science

mo om

pmp

or Or C6H5C6H5

in which the ortho-, meta-, and para- positions of the carbon atoms in the

and

rings are as marked.

Another class of compounds is called condensed-ring or fused-ring systems. These

structures contain two or more aromatic rings that share a pair of carbon atoms.

Examples include naphthalene, anthracene, and phenanthrene, the latter

two

being

isomeric structures.

mador&

(naphthalene) (anthracene) (phenanthrene)

Other polynuclear hydrocarbons may include bridged hydrocarbons, spiro

hydrocarbons, mixed systems containing alicyclic and aromatic rings, and aliphatic

chains, etc. Examples may be found in the

CRC

Handbook

[63,

Section C]. Physical

properties of selected polynuclear aromatic compounds are given in

[49,

9671.

Although many of the aromatic compounds based on benzene have pleasant odors,

they are usually toxic, and some are carcinogenic. Volatile aromatic hydrocarbons

are highly flammable and burn with a luminous, sooty flame. The effects of molecular

size (in simple arenes as well as in substituted aromatics) and of molecular symmetry

(e.g., xylene isomers) are noticeable in physical properties

[48,

212; 49,

375;

50,

411.

Since the hybrid bonds of benzene rings are as stable as the single bonds in

alkanes, aromatic compounds can participate in chemical reactions without disrupting

the ring structure.

Aromatic groups are called aryl groups if they are attached directly

a parent

structure. Common aryl groups are

[phenyl or C6H5

-1

Organic Compounds

Nonhydrocarbon Type

There are numerous families

organic compounds, with structures analogous

hydrocarbons, that contain other atoms (e.g.,

C1) besides C and

Classification is done in accordance with the structural theory on the basis of

functional groups present. The atom or atomic grouping that characterizes a particular

family and also determines the properties of its members is called afunctional

group.

Table

2-42

contains a selected list of common functional groups and examples of

Chemistry

313

Table

2-42

Selected

Functional Groups and Representative Organic Compounds

[58]

Example

Class Functional Group Molecular Formula Compound Name

Alkene

>c=c<

CH,CH

CH,

Propylene

Cyclopropylacetylene

CH2\

CHC

CH2’

Alkyne

-cat-

sec-Butyl alcohol

CHjCH2CHCHj

Alcohol

Ether

-OH

-0-

cH30c6H5

Methylphenyl ether

Ethylene oxide

cHvcHz

/O\

Epoxide

(Oxirane)

Peroxide

-0-o-

(CH3)3COOC(CH3)3

Di-tert-butyl peroxide

-C-H

Aldehyde

C&CHO

Benzaldehyde

-C-

Ketone

CH3COCH3

Acetone

(Methyl ketone)

-C-OH

Carboxylic acid

CgHgCOOH

Benzoic acid

-c-0-

-c\

-c

Ester

Acid anhydride

CHjCOOCHzCHj

Ethyl acetate

(CH3CO)

Acetic anhydride

Halide

Acid halide

-X

-c-x

Trichloromethane

(chloroform)

Benzoyl chloride

Amine

Trimethylamine

314

General Engineering and Science

Table

2-42

(continued)

Example

Functlonal Group Motfsular Formula Compound Name

Class

Ethylene imine

Imine

>C=NH

cH<-7

Nitrile -CSN C6HgCN Benzonitrile

Nitroso

-N=O

meta-Nitrosotoluene

Nitro

Amide

Imide

Isocyanate

Oxime

Mercaptan

(Thiol)

+/O

-N

-c-m2

‘NH

-7’

CH2ONO2

CHClNO2

CH2ON02

CONH2

corn2

-SH

Sulfide

-s-

(Thioether)

Disulfide

-s-s-

‘‘@

‘~03-

Sulfonate

(Salt: of

sulfonic acid)

Organo-metallic

-C---fl

R-Hf

Nitroglycerine

Oxamide

Phthalimide

n-Amyl isocyanate

Benzaldoxime

CgHgSH Phenyl mercaptan

(Thiophenol)

CH3SCH2CH3 Methylethyl sulfide

CH3CH2SSCH2CH3 Ethyldisulfide

Sodium dodecyl sulfonate

(Sodium salt

dodecylsulfonic acid)

2H25s03Na

(m3)*Sn Tetramethyltin

-*-

Mg Br Alkylmagnesium bromide