The preparation of methylamine from ammonium methyl sulphate pdf

236 DENHAM AND KNAPP: THE PREPARATION OF

X X I X -

The

Preparation

of

Meth

ylamirie f r o m Ammonium

Methyl Sulphate.

By WILLIAM SMITH DENHAM and LIONEL FREDERICK KNAPP.

WERNER (T., 1914, 105, 2762), who observed t h a t methylamine is produced when ammonium methyl sulphate is heated, followed acidi- metrically the progress of the change t o temperatures up to 2 7 5 O , and regards i t as being represented essentially by the equation NH4*S0,Me = NH,Me*SO,H, although at temperatures above 240° a small quantity of ethylene is formed owing to a subsidiary reac- tion. H e records the separation under favourable conditions of an 85.6 per cent. yield of methylamine. The methyl sulphates of the substituted ammonium bases behave similarly when heated, and the discoverer suggests t h a t those reactions may be found of prac- tical value for the preparation of t h e substituted methylammonium bases.

The results now communicated, obtained in an investigation of Werner’s reaction undertaken with $he object of utilising it for the preparation of methylamine, indicate t h a t , under t h e conditions observed, the reaction is less simple than represented above, and that, a t any temperature a t which a noticeable transformation of ammonium methyl sulphate occurs, a mixture is produced contain- ing ammonium, methylammonium, dimethylammonium, trimethyl- ammonium, and (probably) tetramethylammonium salts, as, indeed,

i q implied in Werner’s statement t h a t “ t h e further progress and

limit of the isomeric transformation may be expressed by the general equations :

NH2RR’*S04Me = NHIER/Me*SO,H

NHRR’RN *SO,Me = NRR’RWe-SO,H,’’

for,,once some methylamine is produced, t h e melted mass may be considered, as pointed out by Werner, to contain methylamine methyl sulphate among other salts.

METHYLAMINE FROM AMMONIUM METHYL SULPHATE. 237 and trimethylamine (taken together) in the product increases, but the absolute amount of methylamine does not alter very much.

Methylamine is produced when a mixture of t h e sulphate of ammonium, dimethylamine, and trimethylamine is heated, and this supports t h e view t h a t i n the1 melted mass obtained by heating ammonium methyl sulphate, a state of equilibrium is attained or approximated to in which, as expressed by t h e equations

2NH3Me*S04H NH4*SO4H

+

NH,MqSO,H,

2NH2MqS0,H NH3Me.S0,H q- NHMwSO,H,

salts of methylamine, and ammonium are opposed. The addition of ammonium salts to t h e ammonium methyl sulphate may there- fore be expected t o increase t h e yield of methylamine, a n expecta- tion which is in accordance with the fact. When one equivalent of ammonium sulphate was mixed with ammonium methyl sulphate, a distinct improvement was observed in t h e yield of methylamine, but t h e mixture does not melt very readily, and, possibly on &mount of t h e imperfect fusion, t h e yield was not further increased when two equivalents of ammonium sulphate were added. Of the few other ammonium salts which it appeared to be practicable ta use, ammonium benzenesulphonate was chosen. With ammonium methyl sulphate, this salt forms a n easily fusible mixture. from which a greatly increased yield of methylamine, is obtained, whilst the proportion of dimet.hylamine and trimethylamine produced (t'aken together) is greatly diminished.

Th0 possibility t h a t t h e beneficial effect of t h e presence of ammonium benzenesulphonate may be related t o t h e known methyl- atipg action of methyl benzeneaulphonate was not investigated ; although this possibility might account for an increased yield of methylamine, i t does not explain the alteration in t h e relative proportions of methylamine on t h e one hand and dimethylamine and trimethylamine on the other i f we suppose t h e subsequent transformations t o be reversible. No further sulphonation of t h e benzene residue was observed, and t h e improved yield cannot there- fore be ascribed t o a partial removal in this way of free sulphuric acid, the presence of which, indeed, does not appear to be harmful and is probably necessary.

The employment of gaseous ammonia suggeats itself as a means of neutralising the free acid (supposing t h a t desirable) and of supplying a t the same time a n increased concentration of ammonium salts, and an improved yield of methylamine was indeed obtained when ammonia in regulated amounb was admitted t o t h e reaction v w d , but t h e method is inconvenient. A t t h e ordinary temperature, ammonia reacts with amrnunium methyl sulphato

238 DENHAM AND R N A P P : THE PREPARATION O F

with the evolution of heat, probably owing t o the occurrence of the following or some similar reaction,

NH,*SO,Me

+

NH, = NH,*S0,*NH2

+

MeOH, and no methylamine is produced.

It is concluded that, t o obtain the best yield of rnet?hylamine by means of Werner’s reaction, thel ammonium methyl sulphate should be heated f o r one hour and a-half a t 260° or atl a slightly higher temperature, when tshe yield of methylamine is about 27 per cent. of the theoretical yield; when a mixture of ammonium methyl sulphate with two equivalents of ammonium benzenesulphonate is heated under conditions otherwise t h e same, the yield of methyl- amine is nearly 50 per cent. of t h e theoretical.

E X P E R I M E N T A L .

In most of t h e experiments summarised in t h e following tables, 1 / l o t h gram-molecule (12.9 grams) of ammonium methyl sulphate contained in a test-tube was heated in a n oil-bath. Excess of sodium hydroxide was added t o t h e aqueous solution of t h e pro- duct, and the liberated bases were distilled, usually under diminished pressure, into aqueous hydrochloric acid. The h y d r b chloric acid solution of t h e amines was then evaporated, at first on

t h e water-bath under atmospheric pressure, and finally in a vacuum until t h e weight was constant. The dried m a s was extracted twice by boiling with absolute alcohol, using 50 C.C. of alcohol for

t h e first extraction and 25 C.C. for t h e second, and t h e r a i d u e of ammonium chloride was wa~ihed with 25 C.C. of cold alcohol. (When very large quantities of ammonium salts were pr-ent, a preliminary extraction was made with much alcohol, and t h e resi- due from t h e evaporation of t h e solution thus obtained was then extracted as above.) After removing the alcohol by distillation from t h e united alcoholic extracts and washings, t h e residual mix- ture of ammonium chloride and amine hydrochlorides was dried until constant i n weight, and

is

some experiments this residue was

extracted twice by boiling it with chloroform, using 50 C.C. of t h e solvent each time. According t o Bresler (Ann. Chim. anal., 1901, 6, 28; compare Behrend, A n d e m , 1884, 222, 119), methylamine hydrochloride is insoluble in hot chloroform, whilst t h e hydro- chloridm of dimethylamine and trimethylamine dissolve quite readily. When ammonium chloride alone was boiled with 50 0.0. and 25 C.C. of alcohol successively, t h e united extra& gave on

METHYLAMME FROM AMMONIUM METHYL SULPEATE. 239 correction for the ammonium ohloride present. The I f yield ” thus found is employed merely as a conventional method of comparing the results of experiments when more accurate methods of com- parison are not available, for the alcoholic extract contained the hydrochlorides of dimethylamine and trimethylamine, and prob- ably more ammonium chloride than was allowed for. The residue from the extraction with chloroform contained, besides methyl- amine hydrochloride, the ammonium chloride present in the alcoholic extract, and in calculating the

(‘

yield of methylamine ” from t h e quantity of product dissolved by alcohol, but undissolved by chloroform, t h e same weight (0.55 gram) was first deducted. In several experiments, the proportion of methylamine in t h e residue from t h e extraction with chloroform was determined by Francois’ method (Compt. rend., 1907, 144, 857), t h a t is, by fix- ing t h e ammonia with yellow mercurio oxide and titrating the methylamine in the filtrate.

I n each of the experiments of which the results are summarised in this table, a tube containing 20 grams of ammonium methyl sulphate was placed in an oil-bath already heated t o the dwired temperature and removed after thirty minutes, t h e contents of t h e tube being at t h e maximum temperature for periods varying between fifteen and twenty minutes. Two-fifths of t h e product (derived from 8 grams of ammonium methyl sulphate) were used for titration, and from t h e remainder the m i n e hydrochlorides were prepared and extracted with alcohol, .as described above. Although the part of the product treated i n this way was derived from only 12 grams of ammonium methyl sulphate, t h e same approximate correction was made for the ammonium chloride p r e sent as in t h e experiments i n which 12.9 grams were used, since t h e same quantities of alcohol were employed i n t h e extractions. Werner’s results by titration after fifteen minutes’ heating a t nearly equal temperatures are given for comparison. The

‘‘

yields of methylamine ” are expressed as percentages of t h e theoretical yield if complete transformation occurred. The weight of methyl- amine hydrochloride from 12 grams of ammonium methyl sulphate . would then be 6.27 grams.

Effervesceace occurred in all cases, especially in 3 and 4, where the temperatures in t h e t-ubes rose above that of t h e bath, b u t both t h e effervescence and t h e evolution of heat slackened after a few minutes. The fused products from experiments 1 and 2 were slightly yellow; those from 3 and 4 were dark reddish- brown.

TABLE

I.

1.

11.

III.

IV.

V.

Yield

of

methylamine

"

Isomeric

change

"

calculated

from

I11

Yield

of

at

nearly

equal

A

NO.

P

\

Amine

after

correction

rnet,hylamine

temperatures

Period

at

hvdrochloridee

for

NH,Cl.

from

titration.

(Werner].

of

Totd

duration

experi-

of

heating

ment.

Minutes.

1

30

2

30

3

30

4

30

maximum

&solved

by

/

,,

Y

16

min.

at

160-165'

0-61

1.0

2.2

11-5

(160')

18

,,

200-205°

1-17

10.0

23.8

25.8

(200-205')

22

,,

255-260'

3.94

54.1

89.6

85.9

(250-260O)

22

,,

27A275"

4.19

68.1

95.6

97.2

(275')

temperature.

alcohol

(grams).

Per

cent.

of

theoretical

METHYLAMINE FROM AMMONIUM METHYL SULPHATE. 241

TABLE 11.

I n the experiments s u m m a r i d here, the period of heading WBB

longer. 12.9 Grams of ammonium methyl sulphate w0re used for each experiment, t h e theoretical yield of methylamine hydro- chloride being 6-75 grams.

The temperaturee are those of t h e bath, initially at t h e ordinary temperature.

I. 11.

Weight of amine

/ ? hydro-

No. Duration

of of

experi- heating. ment. Hours.

5 100

6

{X

6?2

C&

{:

chlorides dissolved by

alcohol. Temperature, etc. Grams.

100" 0.69

hours up to 168".

hours a t 160-168".) 0.70 hours up to 206". I

hours a t 196-206'. 3'24 hours up to 255'.

hours at 230-2555".

}

3.89

hour up to 272O.

hour at 240-272".

}

4.52

111. Yield of methvl-

amine calculabd from I1 after correction for am-

monium chloride. Percentage of the theoretical yield.

2.1 2.2 39.9

49.6

58.8

Partid Solubility of the A mine Hydrocklorides in Chlsroform. -Table I11 shows t h e proportion of t h e alcohol-solubfe product.

TABLE 111.

12.9 Grams of ammonium methyl sulphate were heated i n each experiment, t h e theoretical yield of methylammonium chloride being 6-75 grams.

I. 11. 111. IV. V.

Yield of Yield of methyl. methyl-

Weight of amine armne

amine calculated calculated hydro. from I1 from I11 chlorides after after Weight of dissolved correction correction

amine by alcohol for em- for Fm-

7*-, hydro- but un- monium momum

No. Duration chlorides dissolved chloride. chloride.

of of dissolved by chloro- ,-A-/

experi- heating. Tempera- by alcohol. form. Percentage of the

ment. Mins. ture. Grams. Grams. theoretical yield.

18 230-234" 3.0 2.1 36.3 23.0

lo

11 17 2 5 6 2 5 8 ' 3.74 2.44 47.3 28-0

12 16 Fromroom

[image:6.360.37.325.74.292.2]

242 DERHAM AND K N A P P : THE PREPARATION O F

found to be insoluble in chloroform. The results are confirmed by those displayed i n later tables. I n experiments 10 and 11, the vessels containing t h e ammonium methyl sulphate were placed in a n oil-bath already heated to t h e required temperature. I n ex- periment 12, the ammonium methyl sulphate was heated in sixteen minutes from the ordinary temperature t o 260°, and then removed from the bath, when t h e temperature of the, melted salt remained at about 260° for a minute or two, and then fell slowly.

Nitrogen in the Still Residzce.-In experiment (10)) after t h e

volatile base8 had been removed by prolonged distillation of t h e alkaline solution of t h e product obtained on heating t h e ammonium methyl sulphate, t h e residue i n t h e distillation flask was neutralised with sulphurio acid and evaporated t o dryness. The dried residue waa found t o contain nitrogen.

Effect of Ammonia on the Transformation.-In experiment (13)

(table IV), a very slow current of ammonia was passed into t h e salt after it had been melted and heated to 1 7 0 O ; in experiment (14), t h e flask containing the salt was heated rapidly to 220°, and then attached to a reservoif of ammonia gas under a pressure of 100 mm., in addition to t h e atmospheric pressure; and i n experi- ments (15), (16), and (17), ammonia, similarly under a slightly increased pressure, was present from t h e beginning. If t h e yield of methylamine were theoretical, and if all the acid formed were neutralised by m m o n i a , t h e total weighta of hydrochlorides i n column I11 would be 12.1 grams (5-35 grams of ammonium chloride and 6.75 grams of methylamine hydrochhide)

.

TABLE

IV.

12.9 Grams of ammonium methyl sulphate were heated in each The oil-bath and contents were heated from t h e experiment.

o r d h a r y temperature. The temperatures are those of the bath.

N O .

of experi-

ment.

13 14 I5

I 6

17

I.

-

Duration of heating.

Hours. Temperature.

34 1+ hours at 234'

34 2 ,, 260'

34 2

.,

260'

29 2 ,, 240'

260'

''

'(redhed 270")

TT.

Weight of amine hydro- chlorides.

Grams. 8.89

7.13 7.48 11.27 12.15

111. Iv.

Yield of methylamifie

calculat'ed

from 111

after correc-

Weight of tion fpr

amine ammomum

hydro- chloride.

chlorides Percentage

dissolved of the

by alcohol. theoretical

Grams. yield.

4-32 55.9

4-93 64.9

5.14 68.0

4- 59 59.9

METHYLAMINE FROM AMMONIUM 'METHYL SULPHATE. 243

Effect of Ammonium S d p h a t e on t h e Transformati-on.-Table V

summarises t h e results of a dtudy of t h e effect on t h e yield of methylamine of the duration of heating aad of t h e presence during the reaction of different proportions of ammonium sulphate. I n this series, t h e percentage of methylamine w w determined by Franpis' method, already referred to, i n t h a t portion of the amine hydrochlorides which was dissolved by alcohol, but undissolved by chloroform

.

Estimation of t h e Dimethylamine and Trimethylamine in the

Chlorof o r m - s o h ble Part .-The following percentaga of dimethyl- amine and trimethylamine hydrochlorides were found i n t h e chloroform-soluble portions abtained in experiments 19 and 24, using Bertheaume's method (Compt. rend., 1910, 160, 1251), t h a t is, by precipitating the trimethylamine as periodide and estimating volumetrically t h e trimethylamine in the precipitate and the dimethylamine in the solution :

D'methylrtmine Trimethvlamine

hydrochloride. hydrochloride.

Per cent. Per cent.

Chloroform-soluble portion

Chloroform-soluble portion fr m experiment 19

...

67.4 64.8

from experiment 24 ... 27.0 31.6

Although the comparison is not complete, since in experiment 28 the percentage of methylamine i n the chloroform-insoluble por- tion was not estimated, the results tabulated above indicate that two equivalents of ammonium benzenesulphonate are as effective

as four. With the larger proportion of ammonium benzene-

sulphonate, t h e mixture did not fuse so readily.

E x a m i n a t i o n of t h e R e s i d d Benzcnesu1phonate.--In experiment 25, t h e amines were liberated by the addition of baryta, the excem of which was removed from the residue in the distilling flask after t h e distillation by means of carbon dioxide. The solution was then evaporated to dryness, and the barium estimated i n the dried product.

Found :

Ba

= 30.7.

(C,H,aSO,),Ba requires Ba = 30.4, and C,H,(SO,),Ba requires B a = 36.7 per cent.

General Comparison of Experiments made a t about 26O0.-In

TABLE

V.

12.9 Grams of ammonium methyl sulphate were heated in each experiment. he equivalent of ammonium sulphate Experiments 18-23 were made simultaneously, using the same oil-bath, which was heated = I /20 mol. = 6.6 grams. from the ordinary temperature. The temperatures are those of the bath. I.

rr.

Weight of

-

No. ammonium Duration e9peri- added. heating. ment. Grams. Hours. Temperature. 18 None 14

3

hour at 260" of sulphate of III. weignli 01 hydro-

chlorides dissolved alcohol. Grams. 4.57 amlne by

Effect of Ammonium Benzenesdphonate on the Transfwrmotion.

TABLE

VI. 18.9 Grams of ammonium methyl sulphate were heated in each experiment, except in experiment 25, where 6.45 The figures shown in the table for experiment 25 are the actual grams were used and other substances in proportion. figures multiplied by two to facilitate comparison. One equivalent of ammonium benzenesulphonate = 17.5 grams. I. 11. Weigh! d (UIMOIllUTI1 No. benzene- of sulphonate

-

em- added. Duration r#at. Grams. of heating. Temperature. #!Jlj 17.5 14 hours 26 35.0 14 ,, 27 35-0 18 min. 28 70.0 14 horn Heated- from ord. temp. 20 min. at

250-260". temp.

66 An. at 250-260". Ammonium methyl sulphate added to ammonium benz-

enesulphonate already

heated to 250-260". Heated from ord. temp. 1 hour at 260-260". Heated from ord. 111. Weight of amme

chlorides dissolved

bY

alcohol. Grams. 4.82

hydro- 6.02 4.52 6.24

IV.

Weight

of

mne hydro- _{chlorides dissolved} alcohol but undissolved chlorof

om.

Grams. 3-68

bY by

V. VI. VII. VIII

.

Percentage Yield of Yield of of methylamine methylamine Yield of methylamine calculated calculated methylamine by from I11 from IV analytical after after analytical estimation correction correction estimation in substanoe for for of (col. IV) ammonium ammonium methylamine undissolved chloride. chloride. (IV and V). chloroform. by. Percentage of theoretical yield. 7.-

by

-

NO. of _ment. 12 11 3 18 29 21 14 15 19 30 22 20 23 24 25 27 26 28

0Xpel.i-

I.

Addition

None.

Y? YY 19

Nose

(closed

vessel).

None. Ammonia. 1 equivalent

(??€€,),SO,. 1 equivalent (NH,),SO, 1 equivalent (NH,),SO,. 2 equivalents (NH,),S04. 10 equivalents (NH,),SO,. 1 equivalent C,H6*S0,NH,. 2 equivalents C,H,*SO,NH,. 4 equivalents C,H,*SOsNH,. YY (closed vessel). YY 9Y 1) 9) TABLE VII. XI. 111. IV. V. VI. From amine hydro- From amine chloride hydro- soluble in chloride alcohol but alcohol chloroform analytical after correc- after correc- estimation soluble in insoluble in BY From tion for tion for of the titra- ammonium ammonium methyl- tion. chloride. chloride. amine. Yield of methylamine as percentage the theoretical yield. Temperature. ord. temp. to 260'.

25A-258'. 22

min. at 255-260'. 45 min. at 260". 1 hour at 250-260'. 2& hours at 260'. 2 hours at 260'. 2 hours at 260'. 45 min. at 260'. 45 min. at 260'. 23 hours at 260'. 45 min. at 260'. 2a hours at 260O. 1 hour at 260". 20 min. at 250-260'.

256-260'. 55

min. at 250-260'. 1 hour at 250-260". - 58.3

-

63.1

-

62.1

-

66.9 -

63.3 58.8

-

66.2 - 71.0

4

30.8 24.6

2

32-4 26.8 33-3 - 36.3 31.5 36.4 27.6 35-6 30.0 34.7 29.6 46.4 - 49.5

-

56.3 48.7 55.4 -

THE BEHAVIOUR O F THE CONSTITUENTS, ETC. 247

Methylamine f r o m a Mixture of the Sulphates of Ammonium,

Dimethylamnwniwm, and Trimethylammolviu/m.--Five grams of the

mixed hydrwhloridee of dimethylamine and trimethylamine, obtained i n the extractions with chloroform, were mixed with an excess of sodium hydroxide solution, and the liberated bases were distilled into an aqueous solution of 6 grams of sulphuric acid. The solution was neutralised with ammonia (but t h e presence of some free acid would doubtless have been advantageous), and t h e residue, after evaporation tlo dryness, was heated a t 270° for a short time. The bases were converted into t h e hydrochloride5 and extracted with alcoho), and then with chloroform, which dissolved 1.55 grams. After purification of the portion insoluble in chloro- form, 0.44 gram of methylamine hydrochloride was obtained.

CHEMICAL LABORATORY,

ST. MARY’S HOSPITAL MEDICAL SCHOOL,