CA1051023A - Method for tobias acid manufacture - Google Patents

Abstract

AN IMPROVED METHOD FOR TOBIAS ACID MANUFACTURE

ABSTRACT OF THE DISCLOSURE
The preparation of Tobias acid by the amination of a salt of Armstrong acid in the presence of ammonia and sulfur dioxide is improved and the amount of beta-naphthyl-amine produced as a byproduct reduced by effecting the reaction under specified reaction conditions.

Description

~.~)5~Z3 BACKGROUND OF THE INVENTION
This invention relates to an improved process for preparing 2-naphthylamine-1-sulfonic acid which may be car-ried out either continuously or batchwise.
~ 5 The preparation of 2-naphthylamine-1-sulfonlc - acid, also referred to herein as Tobias Acid~ by the amina-tion of ~ salt of 2-naphthol-~-sul~onic acld~ or sslts there-' ofg also referred to herein as a salt of Armstrong Acid, in the preseince of ammonium sulfite or ammonia andi sul~ur di- ' oxide, is an example of the well-known Bucherer reaction ~;
which has been carried out industrially for many years. In '~
the industrial proce~s, the reaction which yields Tobias 1 Acid also produce~ 2-naphthylamine (BNA) in amounts ranging '1 from 0.3 to o.6~ by weight, 3,000 to 6,ooo ppm. based on the weight of the Tobia~ Acid isolated. In the Bucherer react-ion the ammonium sulfite æerves as a source of both ammonia ' ;' and sulfur dioxide. - ~
`In describing the proce~s of the sub~ect invent- I
ion~ hereaftèr~,~the term~ ammonia and sulfur dioxide are `~
20 ~ def'lned as total ammonia and total sul~ur dioxide from all potantial sourc~es within the reaction mixture. The Arm-;~
strong Acid's~lt5 re~erred to hereinafter are defined as the alkali metal salt~, or mlxtures thereof. -' ~ OSHA (a) regulations now require that matèrials 1 25 cannot contain more than 0.1~ by~weight (l,OOO ppm) of BNA~
a po~ent carcinog~n~ [See: "The Control of Industrial Bladi -der Tumour~," T. S.`Scot~t and~M. H. C~. Williams, Brit, J.
Industrial Nedicine,~ 14~ 150-163 (1957)o]~ In orùer to meet thls requirement,~Tob~as Acld,~as produced industrially, mu~t underg~ costly post-treatments. ~ -;
Therefore, a need exists for an improved process `
for preparing Tobias Acid in which low levels of BNA are;;

(a)* Occupational Safety and ~ealth Administration ~2 -produced therein and whereby the need for post treatments i5 obviated.
We have discovered that Tobias Acid ~ich contains acceptable levels of BNA may be obtained ln high yield by aminating a salt of Armstrong Acid, and precisely controlling (l)the reaction temperature, ~2) the reaction time, (3~ the mole ratios of total ammoni~ and sulfur dioxide to the salt of Armstrong Acid initially charged, and (4) the lnitial concentration of the ~ .
salt of Armstrong Acid. ~
In accordance with the present invention ~here is provided in a :.:
process for preparing 2-naphthylamine-1-sulfonic acid by reacting an aqueous 10 solu~ion of a salt of 2-naphthol-1-sulfonic acid, a source of ammonia, and : ~:
a source of sulfur dioxide in a sealed reaction vessel and recovering 2-naph-; thylamine-l-sulfonic acid therefrom, the improvement comprising forming an aqueous reaction mixture initially comprising 5 to 50% by weigh~ of said salt of 2-naphthol-1-sulfonic acid, ammonia, and sulfur dioxide wherein the ; mole ratio of said 2-naphthol-1-sulfonic acid salt to total ammonia to sulfur ~ dioxide ranges from 1:4:0.75 to 1:60:30, respectively, with the provisos (1) .. that the mole ratio of ammonia to sulfur dioxide shall be at least 2:1 but not more than 7:1, (2) that the number of moles of sulfur dioxide being not : less than the three quarters (0.75) number of moles of said 2-naphthol-1-sul-fonic acid salt, (3) that ~he solution shall contain at least as many moles of water as the number of moles of sulfur dioxide present, (4) the temperature of the reaction mixture be between about 100C. and 135C., and (5) the reac_ tion mixture is maintained at a temperature from about lOO~C to 135C for a period of time from about 1/6 hour to about 30 hours; and further provided that the initial concentrations of 2-naphthol-1-sulfonic acid salt, ammonia, :
: and sulfur dioxide the reaction time, and reactlon temperature satisfy the :.
followi.ng two equations~
I. The percentage yleld of Tobias Acid = a number greater than 80 = .
01 [1 - te ~3 ~ X 100 II. PPM of BNA = 6.414 x 10 ~2t ~ ~1 ( 1 - e 03t)1 : PERCENTAGE YIELD OF TOBIAS AGID X 03 ~:
PPM of BNA = a number less than 1000 wherein e is the irrational number on which natural or naperian logarithms are ~ ~ -3- .:.
': :`

~s~
based (approxlmately equal to 2.71828), t i~ the tlme in hours, ;~

~ 2 ' ~:

03 = ~ 2 ' [ [11~260~397 T)] ~ [SO233 027 [NH3~
~2 = 30.63 [e ~10~0~0~397 T)3 [So2]3 027 [NH3]-4 394 , T is the absolute temperature ln degrees Kelvin, [S02] is the con~
centration sul~ur dioxide, and [NH33 is the concentration of ammonia = ~ ( k - k ~, ~ t kl - k2) ~ k2 ~
.~ 10 kl ~ 3-182 x lO [e [17~020~397 T-)] ] [SO Jl.817 [NH ~-0.825 k2 = 6.26 x 10 [e [20,950(397 T-)] ] [sO ]5-191 ~NH ]_4-984 Thus, we have discovered that high yields ~greater than 80%) of Tobias Acid containing distinctly lower levels of BNA (less than 1000 ppm) can be obtained by reacting an aqueous solution of a salt of Armstrong Aoid, ammon-i ia and sulfur dioxide in a suitable sealed~pressure vessel at temperatures from ;,' ~ 100~to 135C., preferably from 120 to l30C., for a period from l/6 to 30 j hours, preferably from 1 to 4 hours using precise excesses of ammonia and sulfur dioxide over the salt of Armstrong Acid, as well as precise initial :i:: :
concentrations of said salt of Armstrong Acid, A suitable sealed pressure vessel is one which is constructed of a material substantially inert to the reaction mixture, such as glass, titanium, tantalum, or stainless steel. The :~
reaction time varies depending on~the tempeTature, mole ra~io of total ammonia and sulfur dioxide to salt of Armstrong Acid, and to the initial concentration of said salt of Armstrong Acid~ High initial Armstrong Acid salt concentrations :~ and sulfur dioxide concentrations require generally shorter reaction times and vice versa. Higher total ammonia concentratlons require longer reaction times ;
I ~ and vice versa l~ . After the reaction Dixture has been maintained at:the desired temp~
; erature for a given period o time, work up may be comple~ed by cooling the -~
~; 1 30 vessel rapidly, venting and dis- - :

.~. ........ : -3a-charging the contents. llhe discharged solution is then ~-acidified to precipltate free Tobias Acid which is then `~
separated by filtration, washed and dried.
We have found that lowering the temperature o the reaction mixture from lSS to 125C., or example, re-duces the BNA content of the isolated Tobias Acid from 800- ;
1000 ppm after two post-treatments to only 350-400 ppm `~
without post-treatment.
Concerning the other factors cnumerated herein-above, we have found that the formation of BNA is retarded by moderately l~wering the molo ratio o ammonia iand slight-ly raislng the mole ration of sulfur dloxide relatlve to Arm-strong Acid, or the salts thereo. Running the amination reaction for a shorter time also has a retarding effect on .
the formation o BNA. We have found that the factors named herein are interrelated, and that altering any one of them can affect the quality of the product.
The lnitial concentration of the Armstrong Acid salt m~st be between 5 and 50% of the weight of the reaction mixture, preferably from 20 to 40%; the mole ratios of the Armstrong Acid salt to ammonia to sulfur dioxide may ~ary ;
from 1:4:0~75 to 1:60:30, and is preferably in the`range of 1:6:1.75 to l:lO:S; provided that: ~1) the mole ratio of am-monia to sulfur dio~ide must be at ~east 2:1 but not more thani 7:1, preferably in the range of 2:1 to 4:1, t2) the number of moles of sulfur dioxide must never be less than the three quarters ~0.75~ number of moles of 2-naphthol~
.: ,.
sulfonic acid salt, ~3~ the solution must always contain `~ -at least as many moles o water as the number of moles `~
of sulfur dioxide present, t4~ the temperature of the ~`
~ , ~
'~ ,' ;; ~ .
'''~ .~ '.'" .' ; _ 4 _ ~
;,.,'',~ ~' ~0S~ 3 reaction mixture ranges from about 10~C. to about 1~5C., and (5) the reaction mixture is maintained at said tempera-ture for a period of time from about l/6 hour to about 30 hours.
In addition to beta naphthylamine which arises from side reactions in the conversion of Armstrong Acid to Tobias Acid, any beta naphthol pre~ent as an impuri~y in the Arm-~ strong Acid 1S converted to beta naphthylamine. Thus, it is ; important that the Armstrong Acid salt used as a starting materia1 be as pure as possible. ~ ;
In order for a procqss for the production o~ Tobias Acid to be commercially practical, the yield of product . .
should be at least 80~of theoretical based on starting mat-erial. As noted above, the final product should contain less than l,OOO ppm of the undesirable 9NA side product. By statist~cal analysis of 174~experiments, we have developed two equations~ which relate the yield of Tobiaæ Acid and the yield of BNA produced~by~side reactions to the concentration of the reactants, the reaction time,~and the~reaction temper_ ; 20 ~ ature. Whlle experimental errors may cause any given experi-ment to deviate som~what from the results predicted by the ~ -.
equationj thq equation provides & reliable estimate o~ the l . ., ; , ~
average re~ults~to be expected from several experiments.
' The~percentage yield of ~rmstrong Acid is given by the fol-; 25 ~ lowing equation: ~ ~
PERCENTAGE YIELD 0~ TOBIAS AOID - 0~[1-(e 09 )] X 100 ~ :
wherein e is the irrational number on which natural or nap- -.
erian logarlthms are based (approximately equal to 2.71828), t i8 the time in hours , `~
j . -~0 ~1 ~ 01 3 ~ :

2 ' 0'3 ~ ~31 + 6\a! ~
. ~
~ - 5 -,:

~S~3 = 4.773 ~11,260~ 1 ~ 1 )] [so2]3 027 LNH ] -2.097 E [10~0~0(~ ~ T )~ ~SO2] ~NH3]

T is the ab~olute temperature in degrees Kelvin, ~SO~] is the concentration sul~ur dioxide as defined above (page 2, line l9) in m~les per liter, and ~NH3] is ~he concentration of ammonia as deflned above (pa~e 2~ line l9) in moles per liter.
The amount of BNA iD the Tobias Acid product which arise~ ~rom:sources other than beta naphthol present in the ~:~
- ~tarting material,expressed as ppm by weight,is given by the ~:
~ following equation:
; PPM o~ BNA ~ 6 4I4 x 109 [a~t + ~L~ e~03t)] ;
PERCENThGE ~IELD OF TOBIAS ACID x 03 wherein e, t, [S02], [NH3], T and ~ are as de~ined above and -al=0l(kl-k2), a2 = ~2 (kl ~- k2) ~ k2, and kl=~.la2x~10-~El~7~0~0~ 7F)]][So,]l'817 ~]-0~8Z5 20~ r t20,950(~ 5.~91 ~ .984 kæ=6 . 26 x 10 3 Le ~ J [S02 ~ ~ ;[NH3 ]

, It is important to note that the accuracy o~ these equations has~been~test~d onl~ in the broad range of con~
: 25 ditions ~et out as the limltatlon o~ the present irlvention :
(page 4, lins l9 and f`f ) . Witbin this broad range, the equstion may be us~ed both to predict the results which would;
be obtai~ed~by.conducting the reaction under an~ given con~
; ~ dition, and~:to set:forth the limits of the present invention.
.. :.,;
~, :,:;, ~Sl~)23 ~
The following examples are provided foa~ purpos~s of illustration only and may lnclude particular eatures o the invention but are not limited thereto. Except as other-wise noted, all parts are by welght and temperatures are in degrees centigrade.
Example l This example sho~s the c~ndltions or the paocess o th-~s invention. The reaction is carried out at moderate-ly high temperatuae ~122-126C.) using a dilute solution of starting material, a mole ratlo of A~nstrong Acld, sodium salt:ammonia:sulfur dioxide o 1:20:10, respectively, and a short reaction tlme.
To a suitable pressure vessel are added 2.92 grams ~0.01 mole) o the sodium sa~t of 2 naphthol-l-sulfonic acld ~84.3% real containing 0.002% beta naphthol~, 13.40 gaams ~0.10 mole) of arnrnonium sulfite rnonohydrate, and 18.80 grams of water to prepare an aqueous solutlon contalnlng 7% by ~-` weight of the sodlum salt o A~msta^ong Acid. The clave is sealed and mechanically agitated or one hour at 122-126C.
` 20 The pressure vessel is then cooled and vented, and the con-tents discharged. Analysis of the dlscharge solution shows ~
a BNA level o 189 ppm or 161 ppm 1 allowance is made or ~ -the beta naphthol inltially present and a yleld of lOQ%
Tobias Acid.
Example 2 ;
is example illustrates a preferred process of : .
thîs invention carried out at the same temperature as Exam-ple 1 with a more concentrated solution of starting material, with a mole ratio of Armstro~g Acid, sodium salt:ammonla:

'.~ ` " , : ' .~ ~
: . ~ '.' ,' '~ 0 ~ 1 ~ 2 ~

sulfur dioxide of 1:9:3, respectively, arld a slightl~ loneer reaction tlme. The yield of Tobias Ac.id is reduced and BNA
content is ~.ncreased relative to E~ample 1, but the results ~
are still excellent. ~;
- 5 To a suitable pressure vessel are added 5.84 grams(0.02 mole) of the sodium salt af 2-naphthol-l~sul~onic acid ~:
(84.3~ real containing 0.002~ beta naphthol),:8.04 grams `, - (o.o6 mole) of ammonium sul~ite monohydrate, ~52 gram~ o~ '~concentrate ammonium hydroxide (o.o6 mole) o~ ammonia and ; 10 7.20 grams o~ water to prepare an aqueous so~ution contain~
: ing 20~ by ~eight of the sodium salt of Armstrong Acid. The pressure vessel i8 sealed, mechanically agitated at 122-126C. ~ .
; ~or three hours~ cooled and vented and the contents dlscharg~
ed. Analysis of the contents show a BNA level o~ 330 ppm or , l 15 302 ppm lf allowance is made for the beta naphthol initially 'l ~ , present and a yield o~ 95.8~ of Tobias Acid.
xam,ple 3 ; ~
~ his exampl e shows the proces:s of this invention - . . , carried out at ~he'same temperature and init,ial concent~at- ; ;
~ 20 ~ ~ ion of starting ~material as in Example 2 ~or a longer p~riod ;,, ,, ' , of time with A mole ratio of Armstrong Acid, sodium salt:
ammonia:sulfur dioxide of 1:10:1.75, respectively~ An ex~
, ,1 , ce hent yield,is,obtainëd with an increase.in B~A relative ~, :,1 ,, ' , ~ ~ ' to Example~ 2. ~
; ~ 25 . To ~a sultable pressure vessel are added 5.84 grams ,': ~' (0.02 mole) o.~ the sodium salt of 2-naphthol-1=sul~onic acid ': :
-~ (84.~ real;containlng 0,002~ beta naphtbol), 4.69 grams ~ ~ . (0.035 molè) of ammonium sulfité monohydrate, 7.62 g.ams of .! concentrated ammon1um h~droxide (,0.13 mole of ammonia~ and ~ :' l 30 6.45 grams oD water to prepare a 20% by weight solution of I the sodium,salt o~ Armstrong Acid. The clave is sealed and ' -~ , , .. .
: ~ - 8 - , :. :

. , , ~ . . . . . . . . .

~L~51~23 mechanically agit~ted at 122-126C. ror twenty hours. The pressure vessel is then cooled and ventedJ and the contents discharged, Analysis of the discharge solution shows a ~NA
content of 624 ppm or 596 ppm i~ allowance is made for the beta naphthol initially presen~ and a 98.3~ yield of` Tobias Ac id .
Example 4 T~is example illustrates the process of thi~ in-vention carried out at 102-106C., the lowest temperature investigated, using a molar ratio of Armstrong Acid, sodium salt:ammonia:sul~ur dioxide of 1:10:5~ respectively. While the BNA level is low the yield is somewhat lower than Exam-ples 1-~, although Btill quite acceptable.
To a suitable pre~sure vessel are added 5~84 grams (0.02 mole) o~ the sodium salt o~ 2-naphthol-1-sul~onic acid (84.~ real contalning 0.002% beta naphthol)g 13.40 grams (0.10 mole) of ammonium sulfite monohydrate and 4.15 grams of water to prepare a ?2~ by weight solution of the sodium salt of Armstrong Acid. ~The clave is sealed ~nd mechanical-~20 ly agitated~at 10~2-106C. ~or six hours. The pressure V~9- ~:
~el is then cooled and vented, and thc contents discharged.
Analysis Or the di~charge solution shows a BNA content o~
241 ppm or 213~ppm 1~ ~llowance is made ~or the beta naph-thol initially present and a 91~ yield of Tob:ias Acid.
~ Example 5 Thls example show~ the prosess of this invention carried out at a mole:ratio o~ Armstrong acid ~odium s~lt:
: ammonia:sulfur dioxide o~ 1:9:3 under conditions 31milar ~o :
.. ExRmple 2 with a slightly hlgher starting conc~ntration and . ~
a higher te~eraturel The yleld o~ Tobla~ Acid i9 excellent~
While the BNA level is much hi~her, relative to Example 2, lt is still below 1,000 ppm, : . . . . -To a suitable pressure vessel are added 11.68 grams (0.040 mole) of the sodium salt of 2-naphtol-1-sul-fonic acid (84.3% real containing 0.002% beta naphthol), 16.08 grams (0.12 mole) of ammonium sulfite monohydrate, 7.03 grams concentrated ammonia hydroxide (0.12 mole of ammonia) and 2.17 grams of water to prepare an aqueous sol-ution containing 26.6% by weight of the sodium salt of Arm-strong Acid. The clave is sealed, and mechanically agitated while heating at 133-137°C. for three hours. The pressure vessel is then cooled rapidly by immersion in ice-water and vented, and the contents discharged. Analysis of the dis-charge solution shows a BNA content of 820 ppm of 792 ppm allowing for the beta naphthol initially present and a 100%
yield of Tobias Acid.
Example 6 The following example is similar to Example 2 except that the mole ratio of Armstrong Acid, sodium salt:
ammonia:sulfur dioxide of 1:3:1 is outside of the scope of the process of this invention. The yield of Tobias acid is only 45.6%
To a suitable pressure vessel are added 5.84 grams (0.02 mole) of the sodium salt of 2-naphthol-1-sulfonic acid, 2.68 grams (0.02 mole) of concentrated ammonium hydroxide, and 14.92 grams of water to prepare an aqueous solution con-taining 18.7% by weight of the sodium salt of Armstrong Acid.
The clave is sealed and agitated for four hours at 122-126°C.
The pressure vessel is cooled, vented and discharged. Ana-lysis of the discharge solution shows a BNA content of 338 ppm and a 45.6% yield of Tobias Acid.

1~5~a~23 Example 7 The f ollo~lng example shows that by conducting the reaction at 143-147~C. and using a mole ratio of Arm-strong Acid, sodium salt:ammonia:sulfur diox de of 1:3~
both of which ~actors are outside the scope of the process of this invention, both a low yield of Tobias acid and a very high level of BNA obtained.
To a suitable pressure vessel are added 2.92 ~rams (0,01 mole ) o, the sodium salt of 2-naphthol-1-sulfonic acid :
(~4 .~ rea.l ), 1.~4 ~rams (0.01 mole ) of iammonium sull~ite monohydrate, O . 59 gram of: concentrated ammonium hydroxide (0.01 mole of ammonia) and 27.95 griam9 of water to prepare ;
an aqueous solution containing 7 1/2~ by weight of the sod-ium salt o~ Armstrong A.Cid. The pressure vessel is sealed, mechan~cally agitated ~or twenty hours at 1~5C., cooled, `~
and vented; th~ contents are then discharged. Analysis o`f the dlscharge Golutlon shows a ~NA content o~ 4,8~o ppm ~nd a 47.6% yield o~ TobLas A~ld.
Ex~mple 8 The ~oliowlng~ex~ample is conducted in the same :
manner as Example 7, excep~ that the time o~ reaction is l~ngthened bo forty hours, which is outiside the 9COp~ of this invention. This example shows that the BNA con~ént is .
j ~urther ~ncrèased by prolonged reaction at high temperatures.
. . .
25~ Anal~sis o~ the dischargé solution shows a BNA
e,ontent o~ 6,9~9 ppm ar~d ~a Tobias P~cid yield of 65.9%. ; : .

: This example shows the operation o~ ~he process .
: ~ of this invention using a mole ratio of Armstrong A.cid, sod-ium salt:ammonia:sulfur dioxide of 1:60,20, respectivel~.~
To a suitable pressure vessel are added 2.04 grams :~ (0.007 mole) of the s,odium salt of 2-naphthol-1-sul~onic - ~

1~D5~23 acid containing 0.002~,~ beta naphthol, 1~.76 grams ~0.l4 mole) of ammonium sulfite monohydrate, and ~.21 grams (0~14 ~ :~
mole) of concentrated ammonium hydroxide to prepare an aqueous solution containing 5.9~ b~ weigh~ o~ the sodium . 5 salt of Armstrong Acid. The pressure vessel i9 then sealed and mechanically agitated ~or two hours at 124C. The clave is then cooled and vented, and the contents discharged.
An.alys1s of the discharge solution shows a BNA :
level of 124 ppm or 96 ppm allowing ~or beta nap~thol ini- ;
tially present and a 94.~ yield of Tobias Acid.
~ . ' . ' This exampIe shows the operation o~ the process . . of this invention using ~ mole ratio o~ Armstrong A,cid~ :

sodium salt;ammonia;s~llfur dioxi.de of 1:30:10 respectively. : ~ :

To a suitable pressure vessel are added 2.92 erams ~
i . :
1 ' (O.Ol mole) of the sodium salt of 2-naphthol-l-sul~onic :~ ~ acidj 13.40 grams t lo mole) of ammonium sulfite mono- ~
h~drate, and 5.86~grams (0.10 mole') o~ concentrated ammon~
~ ium hydroxide~to prepare an aqùeous solution containing ll~
; . . 20: : by welght of the sodi.um salt of Armstrong ~cid. The pres-, ~ure ves9el i9 then sealed and mechanically agitated ~or three hours at 122-126C, The clave is then cooled and vented, and the contents discharged.

Analys1s of thè discharge solution ,shows a BNA

level of 48 ppm and a 89.75 yield of Tobias Acid. :~

Examp1e ll -~

: : This example shows th~e process of this invention ~ carried out at 121.5-127.5C. using an initial concentrQt~

;j ion of Armstrong Acid, sodium salt of about ~6% by weight, ~0 and a mole ratio o~ Armstrong Acid, sodium-salt:ammonia:~

~ulfur dioxide of 1;4.66:0.868, respect~velyJ

' - 12 ~

1~ 3 To a suitable pressure vessel are added 9.37 ~rams (0.03 mole) of the sodium salt of 2-naphthol-1-sulfonic ~cid (78.8% real), 3.48 grams (0.026 mole) of ammonium sulrite monohydrate, 5.16 grams of concentrated ammonium hydroxide , ~ 5 (o.o88 mole of ammonia) and 2.~,~ gra~s of water to prepare ;'~
:~ an aqueous solution containing 36% by weight of the sodium salt of Armstrong ~cid. The clave is sealed and mechanical-ly agitated for 27.5 hours at 121.5~127.5C. The pressure vessel is then cooled and vented, and ~he contents dis- :
charged. Anal~sis of the discharge solution shows a BNA : -level of 66~ ppm relative to Tobias ~cid, and~a yield of 9~.4~ of Tobias acid.
~' , E~amPle l?
This example ~h.ow~ the operation of the proces~ of '~
: 15.. , this invention using a mole ratio of Armstrong Acid, sodium . .
: salt:ammonia:sulfur dioxide of 1 4 ~o75~ re~pectlvely~
: To a suitable pressure vessel are added 8.81 grams ~ ' (0.0~ mole~ o~'the sodium salt of 2-naphthol-l-sulfonic acid~ ~ -(ô3~.8j$ rea~ 3.0~ ~grams~ (0~u0225 mole) of ammonium sul:fite ",:' 20 ' '~ monohydrateJ 4.~0 grams o~ concentrated ammonium hydroxide (0.075 mole,of ammonia)'and 3.45 grams of water to prepare `~
~: an aqueous~ solution containing 37.5~ by weig'ht o~ the sodium ~ ;
.
, I salt of Arm~trong Acid. The clave is sealed and mechanical~
, Iy agitated at~ll8-124C. for~27.5 hour~. The pressure ; 25 vessel is cooled and vented, and the contents di~charged.
Analysis of the discharge solution shows a BNA level of 279 ~ :`
: ppm relative~to Tobias Acid and a yield of 89.6~ of Tobias : Acid. ~

This example shows ~the operation o~ the process ' of this invention usine a mole ratio of Armstrong Acid, sod- '~
,~ ~: ium ~alt:ammonia:~ulfur dioxide o~ 1:5:0,925, respectively.

- 13 - : ~
~,......... . : ;

To a suitable pressure Vessel are added 8.81 g~ams ~0.03 mole) of the sodium salt o 2-naphthol-1-sulonic acid ~83.8% real), 3.72 griams ~0.0217 mole) o i~mmonium sulfite monohydrate, 5.513 grams of concentrat0d ammonium hydroxide ~0.095 mol~ o ammonia~ and 2.99 gri~ms of water to prepare an~;
a~ueous solution containing 35% by weight o the sodium salt of Armstrong Acid. ~he clave is sealed and mechanically agitated at 120C. or 29.S hours. The pressure vessel is cooled, vented and the contents discharged. Analysis of the discharge solution shows a BNA level o 440 ppm rela ~ ve to Tobias Acid and a yield o 95% o Tobias Acid. ~j `

. ~ ~ . ..
..' .

-' ;`~'.

,` .

': ` ' -

Claims (5)

The embodiments of the invention in which an exclusive pro-perty or privilege is claimed are described as follows:

1. In a process for preparing 2-naphthylamine-1--sulfonic acid by reacting an aqueous solution of a salt of 2-naphthol-1-sulfonic acid, a source of ammonia, and a source of sulfur dioxide in a sealed reaction vessel and re-covering 2-naphthylamine-1-sulfonic acid therefrom, the im-provement comprising forming an aqueous reaction mixture initially comprising 5 to 50% by weight of said salt of 2--naphthol-1-sulfonic acid, ammonia, and sulfur dioxide where-in the mole ratio of said 2-naphthol-1-sulfonic acid salt to total ammonia to sulfur dioxide ranges from 1:4:0.75 to 1:60:30, respectively, with the provisos (1) that the mole ratio of ammonia to sulfur dioxide shall be at least 2:1 but not more than 7:1, (2) that the number of moles of sulfur dioxide being not less than the three quarters (0.75) number of moles of said 2-naphthol-1-sulfonic acid salt, (3) that the solution whall contain at least as many moles of water as the number of moles of sulfur dioxide present, (4) the temperature of the reaction mixture be between about 100°C.
and 135°C., and (5) the reaction mixture is maintained at a temperature from aboat 100°C. to 135°C. for a period of time from about 1/6 hour to about 30 hours; and further provided that the initial concentrations of 2-naphthol-1-sulfonic acid salt, ammonia, and sulfur dioxide the reaction time, and reaction temperature satisfy the following two equations:
I. The percentage yield of Tobias Acid = a number greater than 80 = ?1 [1 - (e -?3 t)] X 100 II. PPM of BNA = a number less than 1000 wherein e is the irrational number on which natural or nap-erian logarithms are based (approximately equal to 2.71828), t is the time in hours, , ?3 = .theta.1 + .theta.2 , , , T is the absolute temperature in degrees Kelvin, [SO2] is the concentration sulfur dioxide, and [NH3] is the concentration of ammonia .alpha.1 = ?1 ( k1 - k2), .alpha.2 = ?2 ( k1 - k2) + k2 , .

2. A process according to Claim 1 wherein the salt of 2-naphthol-1-sulfonic acid is the sodium salt, where-in the mole ratio of said sodium salt of 2-naphthol-1-sulfonic acid to total ammonia to sulfur dioxide ranges from 1:6:1.75 to 1:10:5, wherein the initial concentration of the said sod-ium salt ranges from 20 to about 40% by weight at the lower ratio and from about 10 to about 30% by weight at the higher ratio, and wherein said solution is heated at a temperature from 120 to 135°C. for a period from about 1/2 to 14 hours for the lower ratio and for a period from about 1/6 to about 8 hours for the higher ratio.

3. A process according to Claim 1 wherein the salt of 2-naphthol-1-sulfonic acid is the sodium salt, where-in the aqueous reaction solution initially comprises a sol-ution containing 20 to 30% by weight of said sodium salt of 2-naphthol-1-sulfonic acid having a mole ratio of said sod-ium salt of 2-naphthol-1-sulfonic acid to total ammonia to sulfur dioxide ranges from 1:8:3 to 1:10:5, and wherein said solution is heated at a temperature ranging from 120 to 130°C. for a period ranging from 2 to 7 hours for the lower ratio and for a period ranging from about 1/3 to about 5 hours for the higher ratio.

4. A process according to Claim 1 wherein the salt of 2-naphthol-1-sulfonic acid is the sodium salt, where-in the mole ratio of said sodium salt of 2-naphthol-1-sul-fonic acid to total ammonia to sulfur dioxide is 1:10:1.75, the temperature is 125°C., the reaction time is 9 to 20 hours and the initial concentration of Armstrong Acid sodium salt is 20%.

5. A process according to Claim 1 wherein the salt of 2-naphthol-1-sulfonic acid is the sodium salt wherein the mole ratio of said sodium salt of 2-naphthol-1--sulfonic acid to total ammonia to sulfur dioxide ranges from 1:4:0.75 to 1:5:1, wherein the initial concentration of the said sodium salt is about 30 to about 35% by weight, and wherein said solution is heated at a temperature from 120 to 130°C. for a period from about 25 to 30 hours.