8/11/2019 Qumica do cloreto de nitrilo.pdf

1/5

1396

J.

Chem. SOC.

A),

1969

Chemistry

of Nitryl

Chloride. Part 1

B y Ram Chand Paul, Darshan Singh , and

K .

C. Malhotra, Department of Chemistry, Panjab University,

Chandigarh-14, India

Nitryl chloride dissolves readily i n sulphuric and disulphuric acids. Cryoscopic, conductometric,and Raman

and

i r spectral studies of its solutions have confirmed t h a t

it

gives

nitronium

ions.

It

forms complexes with strong

electron acceptors like boron trichloride

and

anti.mony pentachloride. From

their

conductance

n

nitromethane and

i r

spectra the complexes have been f ound

to

be ionic.

Nitryl

chloride also forms complexes with organic tertiary

bases.

The ionic nature of these complexes has also been confirmed by conductances

a n d i r

spectra. We con-

clude t h a t nitryl chloride i s a source of nitronium ions rather t h a n positive chlorine, as was postulated earlier.

AN improved method of preparation of nitryl chloride

and its convenient working range (m.p.

-145 ;

b.p.

-15 ) have increased its importance in organic syn-

t l ~ e s i s . ~ ~ ~t is easily hydrolysed and from the products

it has been concluded5 that chlorine is bonded to

oxygen. However, microwave 6 and i.r. spectra

7

indi-

cated

it

to be

a

Y-shaped planar molecule in which

chlorine is attached to nitrogen. The N-Cl bond length

of 1.98 is longer than the sum of two covalent radii.

The N-Cl bond energy8 is 30.0 kcal./mole which is

considerably lower than the normal N-C1 covalent bond

energy of 38.4 kcal./mole.

Thus the N-Cl bond in

nitryl chloride is weaker than normal.

Nitryl chloride

has a low specific conductivity (

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Inorg. Phys. Theor. 1397

room temperature. Excess of nitryl chloride and the

solvent

was

allowed to escape, leaving pale crystals 0.8 .).

These were repeatedly washed with dry carbon tetrachloride

to remove traces of nitryl chloride and were dried

in ucccuu.

They decomposed at 112 (Found: Sb,

3 1 .1 ;

C1, 55.6.

KO,Cl,SbCl, requires Sb

31 -92 ;

C1, 55.94%).

All

attempts

to purify the c ompound failed

as

it was insoluble in most

solvents or reacted with them.

in a trap

at -40'.

Excess of n itryl chloride was added.

chloride can behave as in reactions (3), (a), or 5 )depend-

No&1 -k 2H~S~o,-

N02C1

+

5H2S20,

-- .

N0,Cl + 3H2Sz07-

NO(OH)+Cl

+

HS3010- + H,SO,

(3)

C1++

NO+

+ 2HS O -

+ 4H,SO,

(4)

NO2+

+

HS03C1+ HS,Olo-

+

2H,SO,

5 )

Boron trichloride

1 .0 g.)

was dissolved in sulphur dioxide

The mixture was left a t

-40

for 2 hr. and then brought to

room temperature. The excess

of

nitryl chloride and

sulphur dioxide

was

allowed to escape leaving white crystals

(decomp.

86').

These were repeatedly washed with carbon

tetrachloride and dried

in

uucuo. The

cowplex

could not be

recrystallised as i t is insoluble in the conventional solvents

(Found: B, 5.1; C1,

71.7.

NO,Cl,BCl, requires

B,

5 - 5 2 ;

C1, 7

1.35 ).

Complexes

of

nitryl chloride with organic tertiary bases

were prepared as usual. A known weight of ni tryl chloride

was dissolved in acetonitrile and t o this excess of the base

in acetonitrile was added dropwise with constant stirring.

Pale yellow compounds separated in most cases but some-

times carbon tetrachloride or light petroleum had to be

added to isolate them. The mixtures were left for

1 hr.

and filtered in a dry atmosphere. The solids were re-

peatedly washed with dry carbon tetrachloride and dried

in.

VU CU O .

Analyses are given in Table

3.

Molar conduct-

ances were measured a t 25'.

RESULTS A N D DISCUSSION

By analogy with nitrosyl chloride

l

(NOC1+ NO+

Cl-) one would expect nitryl chloride to yield positive

nitronium ion and negative chloride ion, yet at

low

temperatures in the solid, liquid, and gaseous state

it

reacts with ammonia to yield chloramine and ammonium

nitrite,13J4 suggesting t ha t it gives positive chlorine and

negative nitri te ions. As nitronium

is

a strongly

electrophilic cation,

it

cannot be stabilised in

a

strongly

nucleophilic medium. Therefore the behaviour of

nitrylcliloride was studied in the weakly nucleophilic

sulphuric and disulphuric acids, which can stabilise such

cations.15J6

Nitryl chloride dissolves exothermically in these acids

to give highly conducting solutions.

Its

solubility is

much higher in disulphuric than in sulphuric acid.

Disulphuric acid is itself strongly dissociated and

ionised, and in

it

the bases are completely protonated

as l 7 in

l ) ,

nd the ionisable chlorides are quantitat ively

B

+ 2HzS20,w

BH+

+ HS3OI0- + H,SO,

1)

converted into chlorosulphuric acid as in 2). Nitryl

KC1 +

3HzS207-+

K+

+ HS3010-

+ HS0,Cl + 2H,SO,

2)

A . 3. Burg and G. W. Campbell, J .

A m e r . C h e m .

Soc. 1948,

13 NI. Schmeisser, 2 anorg Chem.,

1948,

255,

33.

14 H. H. Batey and H. H. Sisler, J . A m e r . C h e w .

Suc.

1952,

15 R.

J.

Gillespie and

J.

B. Milne, I n o v g .

Chem.

1966,

5,

1577.

16

J.

Ba n , R.

J.

Gillespie,

R.

Kapoor, and K. C. Malhotra,

70, 1964.

74,

3408.

Canad .

J .

Chern.

1968,

46,

149.

ing upon i ts nature. If it has sufficiently basic oxygen i t

may be protonated by strong acids (equation 3), or if it

is a source

of

positive chlorine ions it may react by

equation (4), or if a source of positive nitronium ion

by equation

5) .

Conductometric and cryoscopic studies

in disulphuric acid show that nitryl chloride behaves

as in reaction 5 ) , so it is a source of nitronium ions

rather than positive chlorine ions. Cryoscopic titrations

of these solutions against sulphur trioxide show that two

moles

of

sulphuric acid are formed per mole

of

nitryl

chloride, in agreement with reaction (5). The Raman

spectrum of

a

concentrated solution of nitryl chloride in

disulphuric acid shows a sharp absorption band at

1400

cm.2 which is characteristic of the nitronium ion in

strongly acidic media.l* The i.r. spectrum of this solu-

tion shows

a

sharp band at

2350

cm.-l indicating nitron-

ium ions.

No

other i.r.-active bands could be observed

for nitronium ions owing to the complicated spectrum

of

disulphuric acid. These observations confirm that

nitryl chloride behaves like potassium chloride in

disulphuric acid.

TABLE

Conductivities a t 25 and freezing points

of

solutions

of nitryl chloride

In R,S,O, In H2S0,

102(Molality)

(ohm-f crm-1) F.p. (ohm-1cm.-l) F.p.

1.0 3.9826 34.98 1.1426 10.17

2.0 4.2792

34-88 1.3184 9-92

3-0 4.5580 34.73 1.6220 9.64

4.0 4.8826 34.60 1.7646 9.35

5 0

5.2383 34-46

1.9888

9-06

6-0 5.5626

34.29

2.2260 8-78

7.0 5,9324 34.12 2.4388 8.46

8.0

6.3045 33-96

2.6400 8.15

9.0 6.6098 33-61 2.7433

7 . 8 0

10.0 6.9523 33.40 2-9406

7.58

12.0

7.6504 33.22 3.1488

14.0 8-2366 32-85

16.0 8.8580 32.43

18.0 9.43 16 32.03

20.0 9-8958 31.60

1 0 3 ~

1 0 K

Unlike nitryl fluoride,lg the solubility

of

nitryl chloride

in

lOOyo

sulphuric acid is limited, so conductance and

cryoscopic studies have been confined (Table 1) to dilute

solutions

(0.12

molal). At low concentration, nitryl

chloride produces

ca 5

particles

(V 5 )

and two ions

of

R. J.

Gillespie and K.

C.

Malhotra,

J . CJzem. SOC

A ) ,1968,

18 R. J. Gillespie, J. B. Milne, and J .

B.

Senior, Inorg. Chem.

l9

G.

Hetherington, D.

R.

Hub, and

P.

L. Robinson,

J .

C h e m

1933.

1966, 5, 1233.

SOC.

955, 4041.

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3/5

1398

J .

Chem. SOC.

A),

1969

high mobility

y

2) in sulphuric acid. (The value of

v is never 5 and

y

is two only at lower concentrations.)

These values steadily decrease at higher concentration

which can be explained if the reaction takes place in

two stages

(6)

and

7).

Reaction

(6)

is irreversible and

N0,Cl

-H2S04 O,+ +

HC1 +

HSOd-

(6)

HC1+ 2H,SO, ----L H3T0 HS0,Cl +

HSO,-

7)

reaction

7)

reversible. Gillespie and his co-workers

2o

have shown tha t hydrogen chloride can be quantitatively

removed from sulphuric acid by a stream of dry nitrogen.

Thus reaction

7)

is never complete

so

values of v and

y

are low. These low values cannot be attr ibu ted to the

formation of ion pairs

(e.g.,

reaction 8) because the

NO2+

HSO,- _ NO,HSO,

8)

dielectric constant of sulphuric acid is high and the

solutions are dilute. There is no evidence that nitryl

chloride reacts

(9)

with hydrogen sulphate to form sul-

phate ions, as postulated by Robinson and his co-

N0,Cl

-

HSO - O,

-

HC1

+

SO

(9)

workers

l9

for nitry l fluoride in sulphuric acid. Since

our solutions are dilute,

y

is not significantly lower than

2.

Dissociation

of

nitryl chloride

as

2N0,Cl

_t N204

k

C1,

in these strong acids is ruled out as

it

would lead to

higher values of

v

and

y

in sulphuric acid owing to

reaction

(10).

We conclude that nitryl chloride ionises

N,O, -

3H2S04--t

NO2+ NOi H 3 + 0 3HS0,-

(10)

in strongly acidic media to produce nitronium ions.

Further information on the nitryl chloride molecule

comes from

a

study of t he coniplexes of nitryl chloride

with Lewis acids and bases. An attempt to isolate its

complexes with Lewis acids at

-75

failed

l4

but the

strong electron acceptor sulphur trioxide forms a complex

NOc,C1,S206, hose structure has not been studied.

We

have isolated complexes with boron trichloride

and

antimony pent achloride in liquid sulphur dioxide.

These complexes are moisture-sensitive and decompose

before melting. Their conductance in nitrobenzene

changes with time, either because of dissociation or

fur ther nitra tion of the solvent. Their solutions in

nitromethane are fairly stable and their molar con-

ductance, comparable with those of uni-univalent

electrolytes, suggests that they are ionic.

Seel and his

co-workers21 obtained similar results for

a

complex of

nitryl chloride and antimony pentachloride in liquid

chlorine. 1.r. spectra also support the ionic nature of

these complexes. The strong fundamental bands

361,

795, and 1685 cm.-l due t o the NO, group are absent

while two new bands a t 2355 and 3760 cm.-l are present.

The band2, at 2355 crn.-l is due to the asymmetric

20 R.

J.

Gillespie

and E. ,4.

Robinson,

J . Amev .

Cheilz.

SOC.,

i965 ,s7 , 2428.

2 1

IT

F. Seel, J . Norgradi, and R. Posse, 2

anovg. Chern.

1952,

269, 198.

stretching vibration of nitronium ion (Table

2).

The

bending mode

(v2)

a t

540

cm.-l has not been observed on

a spectrometer having sodium chloride optics. Accord-

ing to Raman selection rule, nitronium ion must have

TABLE

Principal bands

in

the i.r. spectra of complexes

of

nitryl

chloride and

Lewis

acids

NO,+BCl,-

NO,+SbCI,-

v1

+ v 3 N 0 , + ) .........

3760 w 3750

v,(NO,+) ............... 2360 \-.s. 2355

2v3 BC14)- ............

1460

vl

+ v p +

vQ .........

1380

2vl 2v ............... 1275

vi3 ........................ 690 670

one i.r.-inactive and Raman-active symmetrical stretch-

ing mode at

1400

cm.-l which is absent from the present

spectrum, but the band a t 3760 cm.-l may be the com-

bination tone of this band and

v3 (1400 + 2360).

Simi-

lar observations have been made by Marcus and Fresco

23

in the spectrum of nitric acid and it s solutions in various

solvents. The absence of an absorption band a t 650

shows the absence of N-Cl bonds. All these

absorption bands confirm the presence of nitronium

ions in these complexes. The other bands present are

due to the anions. The broad and strong bands at

1455,

1380,

1275, and

690 cm.-l

are due to the tetra-

chloroborate ions (BC1J-.24 However, for hexachloro-

antiinonate ion (SbClJ-, except for one sharp band at

670

cm.-l

(v3)

no other band was observed because of the

limited transparency of th e optical window. We con-

clude tha t boron trichloride and antimony pentachloride

form

ionic complexes by accepting chloride ions from

nitryl chloride

e.g.,

reactions

11

and

(12),

confirming

that nitryl chloride

is

a source of nitronium ion.

N0,Cl

+

SbC1, NO,Cl,SbClJ

-+

K0&1

+

BC1, __t (N0,C1,BC13) -+

NOZ+-

SbC1,- 11)

KO,-

+ BC1,- (12)

Though acid halides are well known to form addition

complexes with organic tertiary bases, yet no complex

of

nitryl chloride with organic tertiary bases has been

reported. 1.r. spectra of complexes of acid halides and

ter tia ry bases further support the mode of ionisation

of

acid halides. We therefore prepared

a

number of

coin-

plexes

of

nitryl chloride with organic tertiary bases and

oxygenated bases (Table 3). Conductometric titrations

between pyridine, quinoline, rx-picoline, morpholine, and

piperidine and nitryl chloride have been carried out in

acetonitrile to ascertain the stoicheiometry

of

these com-

plexes. There are two breaks in the conductance-

composition curve at molar ratio

1 : 1

and 1

:2,

cor-

responding to NO,Cl,B and

NO,C1,2B.

The initial

22

D. Cook,

S.

J. Kuhn,

and

G. A.

Olah, J .

Chenz. Phys. 1960,

33,

1669.

23 R. A. Marcus and

J. M.

Fresco,

J .

C h e m . Phys. 1957,

27,

564.

24

T. C. Waddington

and

F. Klanberg, J . C h e m .

SOL 1960,

2339.

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Inorg.

Phys.

Theor. 1399

increase in the conductance of the solution is due to the

solubility of the 1 : 1 complex, which may be ionic,

and the decrease beyond 1 :

1

composition is due to the

insolubility of 1 :2 coniplexes. Molar conductances of

these complexes in various solvents (where solubility

permitted) indicate that the complexes are ionic.

How-

ever urea and dimethyl sulphoxide complexes have

conductances below those for

1

:

1

electrolytes,

so

these

complexes are only weakly ionic.

formation of pyridiniuin chloride (PyH)+Cl-,= and in the

complexes of pyridine with selenium tetrachloride 26

and acetyl chloride.27 The bands a t

1620,

1520, 1480,

1360, 1260,

1060, and 760 cm.-l are due to the free

pyridinium ion. A broad band at 2360 cm.-l due

to NO, has shifted to

2150

cm.-l owing to combination

with base. The band

at

1670 cm.-l, which is one

of

the

fundamental bands of the NO, group, has completely

disappeared. We conclude that pyridine combines (13)

TABLE 3

Complexes of nitryl chloride with bases

Colour aiid Molar conduc tance

physical

ALP.

at

25

C1 ( ) C1

( /)

Base ( ) Base

(yo)

Base Stoicheionietry stat e (decomp.) (ohm-1cm. mole-l) Found Required Fou nd Required

Pyridine

Pyridine

Quinoline

a-Picoline

Piperidine

Diethylamine

Triethylamine

Morpholine

Ethylene-

diamine

Dimethyl

sulphoxide

Urea

NO,Cl, (C5H,N)2 Yellow solid

2N0,Cl,C,H5N Pa le yellow

NO,CI,

(C,H,N), Yellowish orange

NO,CI,C,H,N Yellow solid

NO,Cl, (C,H,,N)

,

Yellow solid

NO,Cl[(C,H,),NH], Wh ite solid

NO,Cl[(C,H,),N], Pale yellow

NO,Cl, (C,H,NO) Pa le yellow

NO,CI(C,H,N,), Dark red liquid

NO,CI,

(C,H,SO) I'ellow liquid

SO CI (N,H,CO), Sel low liquid

solid

solid

solid

solid

148'

58

156

164

116

102

90

124

-

-

-

*

In nitroinethane.

Further support of the ionic nature of nitryl chloride is

provided by the spectra of its complexes with organic

tertiary bases. For brevity, only the spectrum of the

pyridine compound (C,H,N),,N02C1 is reported (Table

4).

The spectra of all these complexes indicate that

TABLE

4

1.r.

spectra (cm.-l) of

the

complex of

nitryl chloride

with pyridine

Pyridine

3005s

1583m

1483

1439s

1370vw

1220s

1152s

1072s

1034s

995s

784s

705s

-2ssignnient

C-H

C=C and

C=N

Stretch

C=C

and C=X

C-H in p lane deforniatioii

Pyridine ring breathing

Out-of-ring deformation

NO,Cl, (C,H,K)

2940s

2150111

1620s

1520s

1480s

1360s

1260s

1200s

1

1 7 0 w

1060s

1030w

1010s

930

855vs

7 6 0 ~ s

spectral bands of pure components change on complex

formation. In these complexes absorption bands of

pyridine change similarly to those which occur on the

z5

N.

N. Greenwood and I

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1400

J .

Chem.

SOC. A) , 1969

acid the proton (H+) s a far stronger acid than NO,+ and

hence NO,+ is replaced by the proton in these complexes.

Nitryl chloride can be represented by structures

(111)-(V).

Structure

(VI)

is not reasonable as it

CI CI

I

CI i-

ll

violates Paulings adjacent charge rule and the N-Cl

bond is even longer than ordinary single bonds. Struc-

ture

(111)

(IV)

would be expected t o have a dipole

moment of 2.5

D.

This could be reduced to the reported

0.53

D

if there is a significant contribution of structure

(V). sp

Hybridisation of the chlorine-nitrogen bond

would produce a dipole moment opposite to that of the

NO,

group, which is contrary to the observed value.

Though we cannot draw definite conclusions about the

structure of nitryl chloride from the chemical evidence,

yet we believe that there must be

a

significant contribu-

tion

of

structure (V) to the bond polarities. This is sup-

ported by calculations by Millen and Sinnott

28

of

quadrupole coupling constants, who found that the N-C1

bond in nitryl chloride is

12%

ionic. Therefore, nitryl

chloride can be represented to a fair approximation as

(111)

f p

IV)

- (V). The chlorine atom in nitrosyl

chloride is clearly negative.

In

nitryl chloride the

addition of a second oxygen atom to the nitrogen a tom

considerably reduces its polarity but we conclude that

it has not made it positive.

[8/1751

Received November

18th, 19681

D.

J. Millen and K. M. Sinnott, J . C h e w . SOL 1958, 350.

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