Nitro Displacement Reactions in Aromatic Ether Synthesis | Study notes Analytical Chemistry

Polymer Journal, Vol.

19,

No.

191-202

(1987)

Synthesis

High Performance Aromatic Polymers via

Nucleophilic Nitro Displacement Reaction

TAKEKOSHI

General Electric Company. Research and Development Center,

Schenectady, New York 12301, U.S.A.

(Received August

17,

1986)

ABSTRACT: Nucleophilic displacement reaction

activated aromatic nitro groups with

various nucleophiles

a useful

and

versatile method for the synthesis

aromatic compounds such

as ethers, thioethers

and

other functionalized intermediates

and

polymers. Various strong electron

withdrawing groups can activate aromatic nitro groups. Effective activating groups include cyano,

nitro, sulfone and carbonyl groups such as ester, ketone, anhydride, imide, etc. The reaction

activated nitro compounds with bisphenols

and

bisthiophenols yields bisethers and bisthioethers

from which various aromatic polymers containing ether and sulfide groups can be derived. In many

cases, nitro displacement reactions are essentially quantitative so

that

high molecular weight

polymers are directly prepared by the displacement reaction

difunctional nitro compounds with

bisphenols

bisthiophenols. Another type

unique nitro displacement occurs in the presence

catalytic

amount

a nucleophile

higher temperatures resulting de-nitro coupling

two

molecules

nitro

compound

to form substituted diarylethers.

KEY

WORDS

Nitro Displacement I Aromatic Ether I Dianhydride

Polyarylene Ether I Polyetherimide I Phthalonitrile Ether I

Intensive investigations on high temperature

polymers in recent decades have lead to de-

velopment

a large number

thermo-

oxidatively stable polymers. Basic structures

these polymers are composed

difficult-to-

oxidize "electron sink" such as aromatic rings

with electron-withdrawing groups and het-

eroaromatic system. Polar and rigid struc-

tures

high symmetry associated with such

aromatic ring systems are responsible for gen-

eral lack

adequate processability

these

polymers. More recently, greater efforts have

been made by many researchers in improving

processability

high temperature polymers.

One

the effective approaches toward such

goal

to insert aromatic ether linkages in the

main chains

heteroaromatic systems. In

general, such a structural modification lead to

reduction

energy

internal rotation

the

chains, resulting in lowering glass transition

temperatures and crystalline melting tempera-

tures. As a result the process characteristics

polymers are significantly improved without

greatly sacrificing their thermal stability.

However,

few

convenient synthetic methods

have been available for the formation

aro-

matic ether bonds in high yields. Recently, it

has been shown that certain activated aromatic

nitro groups can be readily displaced by

phenolate and thiophenolate anions to form

various aromatic ethers and thioethers.1.2 In

this article

wish to review recent develop-

ment

nitro displacement reaction in the

synthesis

ether-containing aromatic mono-

mers and polymers.

Nucleophilic displacement reactions

aro-

matic nitro groups have been known for many

years.3 Laubenheimer4•5 described displace-

ment

the nitro group

3,4-dinitrochloro-

benzene by aniline to form 2-nitro-5-

191

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Synthesis of High Performance Aromatic Polymers via

Nucleophilic Nitro Displacement Reaction

T. TAKEKOSHI

KEY WORDS Nitro Displacement I Aromatic Ether I Dianhydride

Polyarylene Ether I Polyetherimide I Phthalonitrile Ether I

Intensive investigations on high temperature

polymers in recent decades have lead to de-

velopment of a large number of thermo-

oxidatively stable polymers. Basic structures of

these polymers are composed of difficult-to-

oxidize "electron sink" such as aromatic rings

with electron-withdrawing groups and het-

eroaromatic system. Polar and rigid struc-

tures of high symmetry associated with such

aromatic ring systems are responsible for gen-

eral lack of adequate processability of these

polymers. More recently, greater efforts have

been made by many researchers in improving

processability of high temperature polymers.

One of the effective approaches toward such

goal is to insert aromatic ether linkages in the

main chains of heteroaromatic systems. In

general, such a structural modification lead to

reduction of energy of internal rotation of the

chains, resulting in lowering glass transition

temperatures and crystalline melting tempera-

tures. As a result the process characteristics of

polymers are significantly improved without

greatly sacrificing their thermal stability.

However, few convenient synthetic methods

have been available for the formation of aro-

matic ether bonds in high yields. Recently, it

has been shown that certain activated aromatic

nitro groups can be readily displaced by

phenolate and thiophenolate anions to form

various aromatic ethers and thioethers.1.2 In

this article we wish to review recent develop-

ment of nitro displacement reaction in the

synthesis of ether-containing aromatic mono-

mers and polymers.

Nucleophilic displacement reactions of aro-

matic nitro groups have been known for many

years. 3 Laubenheimer^4 •^5 described displace-

ment of the nitro group of 3,4-dinitrochloro-

benzene by aniline to form 2-nitro-5-

T. T AKEKOSHI

chlorodiphenylamine. The presence of co-

product, nitrile ion was also confirmed by iso-

lation of 4-aminoazobenzene which was the

coupling product of aniline and benzene-

diazonium cation, the latter was in turn for-

med by the reaction of aniline and nitrous

acid. Interestingly, very little had been de-

scribed on the application of nitro displace-

ment reaction unit! Gorvin 6 demonstrated the

reaction of 2,2' -dibromo-4,4' -dinitrobenzo-

phenone (I) and methoxide as shown in

eq 1.

The reaction was nearly quantitative, indicat-

ing that the nitro groups were far more re-

active than the bromo groups.

The successful result of Gorvin was attrib-

uted to the use of a dipolar aprotic solvent for

the first time. In general, use of dipolar sol-

vents is required in order to attain high yield of

the product at moderate temperatures.

Caswell/ Beck,8- 10 Wirth/ 1- 13 Korn-

blum,14 and Williams 15 - 17 have since shown

that nitrobenzene derivatives with other strong

electron-withdrawing groups undergo nitro

displacement reactions. Among the acti-

vating groups, cyano group was the most

effective followed by N-substituted imide,

keto, and ester groups. Generally, phenolates

used for nitro displacement reactions are re-

quired to be substantially anhydrous. In the