survey of industrial chemestry - chapter 11

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Chapter 11

Derivatives

of the

Basic Aromatics

1. BENZE NE DERIVATIVES

There

are

nine chemicals

in the top 50

that

are

manufactured

from

benzene. These are listed in Table

11.1.

Two of these,

ethy benzene

and

styrene, have already been discussed

in

Chapter

9,

Sections

5 and 6,

since

they are also derivatives of ethylene. Three

others—cumene,

acetone, and

bisphenol A—were covered in Chapter 10, Sections 3-5, when propylene

derivatives were studied. Althou gh the three carbons of acetone do not

formally come from benzene, its primary manufacturing method is from

cumene, which

is

made

by

reaction

of

benzene

and

prop ylene. These

compounds need not be discussed further at this po int. That leaves pheno l,

cyclohexane,

adipic acid, and nitrobenzene. Figu re

11.1

summarizes the

synthesis of important chemicals made from benzene. Cap rolactam is the

monomer for nylon 6 and is included because of it im portance.

Table

11.1 Benzene

Derivatives in the Top 50

Ethylbenzene

Styrene

Cumene

Phenol

Acetone

Bisphenol A

Cyclohexane

Adipic acid

Nitrobenzene



benzene

cumene

phenol

acetone

bisphenol A

ethylbenzene

styrene

cyclohexane

adipic

acid

caprolactam

nitrobenzene

aniline

Figure

11.1

Synthesis of benzene derivatives.



2.

PHENOL CARBOLIC ACID)

The major manufacturing

process

for making phenol was discussed in

Chapter 10, Section 4, since it is the co-product with acetone from the acid-

catalyzed rearrangement

of

cumene hydroperoxide.

The

student should

review this

process.

It accounts for 95% of the total phenol produ ction and

has

dominated phenol chemistry since

the

early 1950s.

Bu t a few

other

syntheses deserve some mention.

A

historically important

method, first

used about 1900,

is

sulfonation

of

benzene followed

by

desu lfonation with caustic. This

is

classic aromatic

chemistry.

In

1924

a

chlorination route

was

discovered. Both

the

sulfonation

and chlorination reactions are good examples of electrophilic

aromatic substitution on an aromatic ring. K now the m echan ism of these

reactions. These routes

are no

longer used commercially.

high pressure

A minor route, which

now

accounts

for 2% of

phenol,

takes

advantage

of

the usual surplus of toluene

from

petroleum

refining.

Oxidation with a

number of reagents gives benzoic acid. Fu rther oxidation to p-

hydroxybenzoic

acid and

decarboxylation yields phe nol. Here phenol

competes with benzene manufacture, also made from toluene when the

surplus is large. The last 2% o f phen ol comes

from

distillation of petroleum

and coal gasification.

Cu

benzoate



Table 11.2

Uses

of Phenol

Bisphenol

A 35%

Phen olic resins

34

Caprolactam 15

Aniline

5

Xylenols

5

Alkylphenols 5

Miscellaneous 1

Source: Chemical

Profiles

Table 11.2 outlines

the

uses

of

phenol.

W e

will consider

the

details

of

phenol uses in later chapters. Phenol-forma ldehyde polym ers (pheno lics)

have

a

primary

use as the

adhesive

in

plywood formulations.

W e

have

already studied

the

synthesis

of

bisphenol

A from

phenol

and acetone.

Phenol's

use in

detergent synthesis

to

make

alky

phenols will

be

discussed

later. Caprolactam

and

aniline

are

mentioned

in the

following sections

in

this chapter.

Although phenol ranked thirty-fourth in 1995, it is still the highest ranked

derivative of benzene other than those using ethylene or propylene along

with benzene.

Its

2000 price

was

38C/lb. That gives

a

total commercial

value of $1.6 billion for the 4.2 billion Ib produced.

3.

CYCLOHEXANE HEXAHYDROBENZENE,

HEXAMETHYLENE)

Benzene can be quantitatively transformed into cyclohexane by

hydrogenation over either a nick el or platinu m catalyst. This reaction is

carried

out at 21 O

0

C and

350-500

psi, sometimes in several reactors placed

in series. The yield is over 99%.



Although many catalytic reactions are not well understood, a large

amount of

work

has

been done

on

hydrogenations

of

double bonds.

The

metal surface acts as a source of electrons. The

bonds as well as hydrogen

atoms are boun d to this surface. Then the hydrogen atoms react with the

complexed

carbons

one at a

time

to

form

new C—H

bonds.

No

reaction

occurs without

the

metal surface.

The

metal

in effect

avoids what would

otherwise have to be a free radical mechanism that would require

considerably m ore energy. The m echanism is outlined as follows.

Table

11.3

shows the main uses of cyclohexane. A dip ic acid is used to

manufacture nylon 6,6,

th e

major nylon used currently

in the

U.S.

Caprolactam is the monomer for nylon 6, for which there is a growing

market.

4.

ADIPIC ACID

1,6-HEXANDIOIC

ACID)

Nearly

all the

adipic acid m anufactured, 98%,

is

made from cyclohexane

by

oxidation. Air oxidation of cyclohexane with a cobalt or m anganese (II)

naphthenate or

acetate

catalyst at 125-16O

0

C and 50-250 psi pressures gives

a m ixture of cyclohexanone and cyclohexanol. Benzoyl peroxide is another

Table 11.3 Uses

o f

C yclohexane

Ad ipic acid

55%

Caprolactam 26

Miscellaneous 19

Source: Chemical Profiles



possible catalyst. The yield is 75-80% because of some ring opening and

other further oxidation that takes place. The cyclohexanone/cyclohexanol

mixture (sometimes referred

to as

ketone-alcohol,

K A

mixture,

or mixed

oil")

is further

oxidized with

50%

nitric acid with am m onium vanadate

and

copper present

as

ca talysts

at

50-9O

0

C

and 15-60 psi for

10-30 m in.

1:3 mixed oil

The mechanism of cyclohexane oxidation involves cyclohexane

hydroperoxide

as a key

intermediate.

then (2), (3), (2), (3),

etc.

The cyclohexane hydroperoxide then undergoes

a

one-electron transfer

with

cobalt

or

m angan ese (II). C hain

transfer of the

cyclohexyloxyl radical

gives

cyclohexanol

or

p-scission gives cyclohexanone.

to step (6) or (7)



Figure 11.2 shows a cyclohexane oxidation reactor. The further

oxidation

of the ketone and alcohol to adipic acid is very com plex but occurs

in good yield, 94%, despite some succinic and glutaric acid by-products

being

formed

because

the

adipic acid

can be

preferentially crystallized

and

centrifuged.

A small amount of adipic acid, 2%, is made by hydrogenation of phenol

with

a palladium or nickel catalyst

(15O

0

C,

50 psi) to the mixed oil, then

nitric

acid oxidation

to

adipic acid.

If

palladium

is

used, more

cyclohexanone is formed. Although th e pheno l route for m aking adipic acid

is

not

economically advantageous because phenol

is

more expensive than

benzene, the

phe nol conversion

to

greater cyclohexanone percentages

can be

used successfully for caprolactam m anu factu re (see next section), w here

cyclohexanone is necessary.

to step (3)

to step (2)

caprolactam



Figure

11.2

The

large tower

on the

right

is the

cyclohexane oxidation chamber

and

purification un i t to convert cyclohexane to the hydroperoxide and then to

cyclohexanone/cyclohexanol. An elevator leads to the top platform of this narrow tower,

where an impressive view of this and other surrounding plants can be obtained.

(Courtesy of Du Pont)

Table 11.4 gives

the

uses

of

adipic acid.

As

will

be

seen later, nylon

6,6

has large markets in textiles, carpets, and tire cords. It is made by reaction

of

HMD A

and

adipic acid.



Table

11.4 Uses

of Ad ipic Acid

Nylon 6,6 fibers 72%

Nylon 6,6

resins

18

Polyurethanes 5

Plasticizer

3

Miscellaneous

2

Source: Chemical Profiles

adipic acid

HMDA

nylon

6,6

C PROL CT M

The

common name caprolactam comes

from

the

original name

for the

Ce

carboxylic

acid, caproic acid. Caprolactam

is the

cyclic amide (lactam)

of 6-

aminocaproic acid. Its m anu facture is from cyclohexanone, made usually

from cyclohexane (58%), but also available from phenol (42%). Some of

the

cyclohexanol

in cyclohexanone/cyclohexanol

mixtures

can be

converted

to cyclohexanone by a ZnO catalyst at 40O

0

C. Then the cyclohexanone is

converted into the oxime w ith h ydroxylamine. The oxime undergoes a very

famous

acid-catalyzed reaction called

the

Beckmann rearrangement

to

give

caprolactam. Sulfuric acid at 100-12O

0

C is common but phosphoric acid is

also used, since after treatment with ammonia

the

by-product becomes



The student should adapt this general mechanism and work through the

specific

cyclic example of cyclohexanone oxime to caprolactam. Note that

the result of the

shift

is an expansion of the ring size in the final amide

product w ith the incorporation of the nitrogen atom as part of the ring.

All

of the

caprolactam goes into nylon

6

manufacture, especially

fibers

(80%)

and

plastic resin

and film

(20%). Although nylon

6,6 is

still

th e

more

important nylon in this country (about 2:1) and in the U.K., nylon 6 is

growing rapidly, especially

in

certain markets such

as

nylon

carpets. In

other countries, for example, Japan, nylon 6 is m ore predom inant. N ylon 6

is made directly from caprolactam by heating with a catalytic amount of

water.

6.

NITROBENZENE

Aniline is an important derivative of benzene that can be made in two

steps by nitration to nitrobenzene and either catalytic hydrogenation or

acidic metal reduction

to

an iline. Both steps occur

in

excellent yield.

Almost all nitrobenzene manufactured (97%) is directly converted into

aniline. The nitration of benzene with mixed acids is an example of an

electrophilic aromatic substitution involving the nitronium ion as the

attacking species. The hydrogenation of nitrobenzene has replaced the iron-

eaction

catalyst

aniline



acid reduction

process. At one

time

the

special crystalline structure

of the

Fe

3

O

4

formed as a by-product in the latter process made it unique for use in

pigments. Bu t the demand for this pigment was not great enough to justify

continued use of this older method of manufacturing aniline.

The

uses

of

aniline obtained

from

nitrobenzene

are

given

in

Table

11.5.

Aniline's

use in the

rubber industry

is in the

manufacture

of

various

vulcanization accelerators and age

resistors.

By far the most important and

growing use for aniline is in the manufacture

of/7,^-methylene

diphenyl

diisocyanate (MDI), which

is

polymerized with

a

diol

to

give

a

polyurethane.

Mechanism

Table 11.5 Uses

of

Anil ine

M DI 80%

Rubber-processing

chemicals

11

Herbicides 3

Dyes and pigments 3

Specialty fibers 2

Miscellaneous

1

Source: Chemical

Profiles

M DA

M DI



Two

moles of aniline react with formaldehyde to give

p p-

methylenedianiline (MDA). M DA reacts with phosgene to give MDI. The

student should develop

the

mechanism

of

this electrophilic aromatic

substitution.

W e

have already been introduced to polyurethane chemistry in Chapter

10, Section 2, where we used toluene diisocyanate (TDI) reacting with a diol

to

give

a

polyurethane.

Polyurethanes

derived

from MDI are

more rigid than

those from TDI. New app lications for these rigid foams are in home

insulation and exterior au tobody parts. The interm ediate M DA is now on the

"Reasonably Anticipated to Be Human Carcinogens" list and the effect of

this action

on the

market

for MDI

remains

to be

seen.

The

TLV-TWA

values for MDA and MDI are some of the lowest of the chemicals we have

discussed, being

0.1 and

0.005

ppm

respectively.

7. TOLUENE DERIVATIVES

Other than benzene, 30% of which is made from toluene by the

hydrodealkylation process, there

are no

other

top 50

chem icals d erived

from

para

only

Figure

11.3 Conversion of toluene to

other

aromatic compou nds.

zeolites

para only

catalyst



toluene

in

large amounts.

However, a few

important chemicals

are

made

from

toluene. As we learned earlier in this chapter, Section 2, a very small

amount of phenol is made from toluene. Toluene also provides an alternate

source that

is

becoming more popular

for the

xylenes, especially

/?-xylene.

These

routes are indicated in Fig.

11.3.

The first example, the

disproportionation of toluene to benzene and the xylenes, is being used in the

U.S. to the extent of 3-4 billion Ib of benzene and xylenes. The last two

examples provide routes respectively to terephthalic acid and

/?-xylene

without the need for an isomer separation, a very appealing use for toluene

that

is often in excess

supply

as

compared

to the

xylenes.

Two

other derivatives

of

toluene

are the

important explosive

trinitrotoluene (TNT) and the polyurethane monomer toluene diisocyanate

(TDI). TNT requires complete nitration of toluene. TDI is derived

from

a

mixture of dinitrotoluenes (usually 80%

o p

and 20% 0,0 by reduction to the

diamine and reaction with phosgene to the diisocyanate. TDI is made into

flexible

foam

polyurethanes

for

cushioning

in fu rniture

(35%), transportation

(25%), carpet underlay (20%),

and

bedding

(10%). A

small amount

is

used

in polyurethane coatings, rigid foams, and elastomers.

TNT TDI

Finally, benzaldehyde, an ingredient in

flavors

and

perfumes,

is made by

dichlorination of toluene (free radically via the easily formed benzyl radical)

followed

by hydrolysis.



benzaldehyde

8.

TEREPHTHALIC ACID AND DIMETHYL

TEREPHTHALATE

TA,

TPA

5

or PTA DMT

There are only two top 50 chemicals, terephthalic acid and dimethyl

terephthalate, derived from /?-xylene and none from

o-

or w-xylene. But

phthalic anhydride is made in large amounts

from o-xylene.

Terephthalic acid

is

commonly abbreviated

TA or

TPA.

The

abbreviation

PTA (P =

pure)

is

reserved

for the

product

of 99%

purity

fo r

polyester m anufa cture. For many

years

polyesters had to be made from

dimethyl terephthalate (DMT) because

the

acid could

not be

made pure

enough eco nom ically.

Now

either

can be

used.

TA is

made

by air

oxidation

of/7-xylene in acetic acid as a solvent in the presence of cobalt, manganese,

and bromide ions as

catalysts

at 20O

0

C and 400 psi. TA of 99.6% pu rity is

formed

in 90%

yield. This

is

called

the

Amoco process.

A

partial mechanism with some intermediates is given on the next page.

Details are similar to the cyclohexane to cyclohexanonexyclohexanol

process discussed

in

this chapter, Section

4.



The

crude

TA is

cooled

and

crystallized.

The

acetic acid

and

xylene

are

evaporated and the TA is washed with hot water to remove traces of the

catalyst

and

acetic acid. Some

/7-formylbenzoic

acid

is

present

as an

impurity from

incomplete oxidation. This is most easily removed by

hydrogenation

to

/7-methylbenzoic

acid and recrystallization of the TA to

give 99.9% PTA, which is a polyester-grade product, mp > 30O

0

C .

p-formylbenzoic

acid /?-methylbenzoic acid

DMT can be

made

from

crude

TA or from /?-xylene

directly.

Esterification

of TA

with methanol occurs under

sulfuric

acid catalysis.

Direct oxidation

of

/?-xylene with methanol present utilizes copper

and

manganese salt catalysis.



Table

11.6 Uses of

TA/DMT

Polyester fiber 50%

Polyester resin

33

Polyester

film 8

Miscellaneous

9

Source:

Chemical

Profiles

DMT must be carefully purified via a five-column distillation system, bp

288

0

C,

m p

1 41

0

C. The

present

distribution

of the TA/DMT

market

in the

U.S. is 44:56. All new plants will probably m ake terephthalic acid.

Table 11.6 shows the uses of TA/DMT. TA or DM T is usually reacted

with ethylene glycol to give poly(ethylene terephthalate) (90%) but

sometimes it is combined with 1,4-butanediol to yield poly(butylene

terephthalate). Polyester fibers

are

used

in the

textile industry. Films

find

applications as magnetic tapes, electrical insulation, photographic film, and

packaging. Polyester bottles, especially in the

soft

drink market, are

growing rapidly in demand.

9. PHTHALIC ANHY DRIDE

The manufacturing method of making phthalic anhydride has been

changing rapidly similar to the switchover in m aking maleic anhydride. In

1983

28% of phthalic anhydride came

from

naphthalene, 72% from o-



xylene.

No

naphthalene-based plants were open

in

1989.

In

1993

naphthalene

rebounded and was used to m ake 20% of the phthalic anhyd ride

again because of a price increase for o-xylene, but as of 1998 no phthalic

anhydride is

made

from

nap hthalen e. Despite

th e

better yield

in the

naphthalene

process, energetic factors make th is less favo rable econo m ically

compared to the

oxylene

route.

The uses of phthalic anhydride include plasticizers (53%), unsaturated

polyester resins

(22%), and alkyd

resins (15%).

Phthalic anhydride reacts with alcohols such

as

2-ethylhexanol

to

form

liquids

that impart great flexibility when added to many plastics without

hurting their strength. M ost of these plasticizers, abou t 80%, are for

poly(vinyl chloride) flexibility. Dioc tyl ph thalate (DOP ), also called di-(2-

ethylhexyl)phthalate (DEHP),

is a

comm on plasticizer.

2-ethylhexanol

DOP or

D E H P

High doses

of

DEHP have been found

to

cause liver cancer

in

rats

and

mice

and it is on the "Reasonably Anticipated to Be Human Carcinogens"

list. In 2000 a report by the National Toxicology P rogram found serious

concern that DEHP in vinyl medical devices may harm the reproductive

organs

of

critically

ill and

premature male

infants

exposed du ring m edical

treatm ent. They also expressed concern that dev elopm ent of male unborn

babies wo uld be harm ed by the pregnant mo thers' exposure to DEHP or that



the child would be harmed by other DEHP exposure during the first few

years

of life.

Certain plasticizer

applications,

such

as

those

in

infants '

pacifiers and squeeze toys, as well as blood bags, respiratory masks, oxygen

tubing, and

intravenous bags softened with DEHP,

may be

affected

in the

years ahead. O ther diesters of phthalic anhydride do not seem to have th e

toxic effects of DEHP so substitutes shou ld be easy to find.

Suggested Readings

Chemical

Profiles in Ch emical Marketing Reporter 3-2-98,

4-13-98, 6-8-98,

6-15-98, 7-6-98, 2-8-99, 2-15-99, and 3-29-99.

Kent,

RiegeVs

Handbook

of

Industrial Chemistry

pp.

849-862.

Szmant, Organic Building Blocks of the Chemical Industry pp.

407-574.

Wiseman,

Petrochemicals

pp. 101-140.

Wittcoff

and

Reuben,

Industrial Organic Chem icals

pp.

234-293.

survey of industrial chemestry - chapter 11

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