Note: Descriptions are shown in the official language in which they were submitted.
106~334
The present invention relates to the preparation
of azo pigments and more particularly to a me~hod for
the automatic control of azo coupling processes in the
manufacture of azo pigments.
In the well-k~own azo eoupling process a diazonium
salt is reacted with a suitable coupling component to give
an azo compound as illustrated by the following e~uation:
R1 N~- NCl- R H ~ R1- N=N ~2 ~ HCl
(diazonium salt~ (eoupling component) (azo compound) ~
~ .
wherein Rl and R are suitable radicals.
; The reaction i9 normally carried out in aqueous
eonditions and proceeds almost quantltatively. It i9
important that the two components come together i~ the
~orreet ratio otherwise quality of the final product suffers.
If too mueh diazonium salt is added the excess which is
usua~ fairly unstable can give rise to decomposition products
which usually cause dirtiness of shade. If too much of
the coupling component is added this is either washed down
the drain during the final filtration and so is wasted, or
it ls le~t in the produet where it can cause eolouristie
wealuless or other property defects.
~ he COUpliIlg reaction in azo pigment manufacture is
carried out in three main ways.
e dlazonium salt, as an aqueous solution or suspension,
is run into a solution or suspension of the coupling
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1C9~1334
component. l~e pH is controlled within
; oertain limits, specific ror each pi~llent, either by
having a buffering agent present or by continuously
measuring the pH with a pH meter and adding acid
or alkali to maintain the pH within the prescribed
limitsO
(2) The coupling component solution is run into a
solution or suspension of the diazonium sal~. The pH
in this case i9 normally controlled by a buf~ering
agent added to the diazonium salt.
.
~) 'rhe dia~o solution or suspension and coupling
~ component solu-tion are added together to the reaction
vessel controlling the rates normally so that the two
I components are always present together in the correct
,~ ratio to give complete reaction. The pH i9 monitored
with a p~ meter and contro1led by the addition of
acid or alkali as required.
Control of the cou~ling process is normally carried
out manually uslng chemical spot tcsts to chack on the
progress of the reaction. The operator carries out these
tests at regular intervals during the reaction and manually
~ ~ .
!~ adjusts the valves controlling the additions of ~he reagents
;~~, to give the required conditions. ~iuch depends on the
operator~s skill and application as to how well this is
carried ou~ and it is inevitable that variations occur.
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~:P6~334 -
Operating und~r batchwisc conditions these
variations can usually be accommodated by modifying
the process *rom batch to batch to compensate f'or them.
Working on a continuous basis this becomes impossible
and ~t is necessary to maintain reaction conditions
constant in order to obtain consistent quality in the
product.
~he automatic controi Or azo coupling has been
described in '
a) Chimia 15 - 1961 - January, pages 1~6 to 163 :in
which excess o~ diazo component i9 detected b~ a potentio-
mctric method using a quinhydrone electrode.
b) British Patent Specification 192~6,720 which clescrlbe~s
the use oP a polarographic method for the control of
azo coupling reactions again by the detection of excess
of the diazo component.
The presence of excess diazo component during an
azo coupling process is often undesirable since the cleanliness
o~ shade of the product can be affected~
We have de~ised a system which gives a continuous
quantitative indication of co~ditions in the reaction vessel
by using an automatic chemical analyser incorporating a
dialyser module to continuously monitor the amount of excess
of the diazo or coupling co~.ponent in the reaction. This
system has the advantage of avoiding the presence of excess
diazo component in the coup-ing process in those cases when
this would be detrimental to the product.
.
~ .
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.. . . .
f~
3LOG1334
.
In certai.~ couplings, however, notably i.n cases when
the solubility of the coupling component is ve~y low, an
excess of diaz,o component is present throughout coupling and
in these cases the reaction can be monitored by continuously
determining the concentration of diazo component present.
If,an excess of diazo component persists the analyser will
show positively whether or not the reaction has stopped and
whether or not it is necessary to add further coupling component
to complete the reaction. : ' -
.. . . . . _. . . .
According to the present in~ention there is pro~ided '
an,azo pigment coupling process in which the a~ount of excess
diazo or coupling component is continuousl~ monitored and the
ad~lition of diazo compon~nt or coup].in~ component to the
reaction is ~utomatically controlled by means of an automatic
chemical analyser incorporating a dialyser module.
The diazonium salt used in the coupling process may be
prepared from any diazotisable amine which on coupling ~ith a
suitable coupling component results in a water-inso'luble azo
pigment. Such diazotisable amines are for example primary
aromatic monoamines or diamines derived from benzen~, or from
biph~nyl, or from condensed benzenoid structures such as
naphthalene or anthracene, or ~rom structures in which benæene
i9 condensed with a heterocyclic ring such as quinoline.
The carbocycl'ic or heterocyclic aromatic nucleus of these
amines can be unsubstituted, or substituted with one Qr more of the
follQwing grQups: .al~yl9 alkoxy, halo~no, ni-tro, cyano) acylamino9
. .
~3L334
sulphonamido, carboxy-alkyl, and carboxylic acid. Suitable amines may be
mono-ni~roanilines, dinitroanilines, nitrotoluidines, nitroanisidines, mono-
chloranilines, dichloranilines, trichloranilines, chlorotoluldines, chloranlsi-
dines, chloronitroanilinesJ benzldine, dichlorbenzidines9 tetrachlorbenzidines,
; tolidines, dianisidines and dichlordianisidines, for example, N-phenyl-3-amino-
phthalimide,5-amino-6-methyl-benzimidazolone, 6-methyl-7-amino-phenomorpholone
(3), 4-methyl-6-chloro-7-aminoquinolone, 4~-2'-methoxy-4'-amino-5'-chlorophenyl-j" amino)-quinazoline, 3-aminodibenzofuran.
The coupling component may be any coupling component normally used
for the production of azo pigments which is able to dissolve to some extent
; in the coupling medium and which couples wlth a suitable diazonium salt to
give a water-insoluble product. Such components are for example acetoacetani-
lide and derivatives thereof such as acetoacet-2-toluidide, acetoacet-4-tolu-
idide, acetoacet-2-anisidide, acetoacet-2-chloranilide, acetoacet-2:4-dimethyl-
anilide, acetoacet-2:5-dimethoxy-4-chloranilide; l-aryl pyrazolones such as
l-phenyl-3-methyl-5-pyrazolone, 1-4'-tolyl-3-methyl-5-pyrazolone, and l-phenyl-
3-carbethoxy-5-pyrazolone; 2-naphthol; 2-hydroxy-3-naphthoic acid and arylides
thereof such as (2',3'-hydr~xy-naphthoylamino)-benzene, 1-(2',3'-hydroxy-
naphthoylamino)-2-methyl benzene, 1-(2',3' hydroxynaphthoylamino)-2,4-di-
methoxy-5-chloro-benzene, and 1-(2',3' hydroxynaphthoylamino)-2-methyl-5-
chloro-benzene, 4-hydroxycoumarin, barbituric acid, 2,4-dihydroxyquinoline,
~, 4-hydroxy-N-methyl-quinolone, 4-methyl-7-acetoacetamido-quinolone, 7-aceto-
acetamido-phenomorpholone (3), 5-acetoacetamido-benzimidazolone.
. .
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1061334
An example of a suitable automatlc chemical analyser
is the Technicon AutoAnalyser (Auto~;nalyser is a Registered
l`rademark).
The AutoAnalyser is a train of interconnected modules
that automate the step-by-step procedures of manual analysis~
In AutoAnalysis, chemical reactions take place in continuously
flowing air-segmented streams. The ~Low of streams is directed
through tubing from module to module,each of ~ich automatically
carries out a different analytical function such as sampling
of un~nowns and standards; metering of reagents; purlfication
and filtration; heating and incubation and detection and
recording.
~ he process of the present invention is f'urther descrihed
by way of Example wlth re~erence to and ~s illus-trated by
Figure 1 of the drawlngs accompanying the provisional
specif`ication which is a schematic flow sketch.
A proportionating pump 10 continuously samples the
pigment slurry through channel 11 from the reaction vessel.
Air in channel 12 is pumped in and this segments the pigment
alurry in channel 11 which theD passes through a dialyser 13
on one side of the dialyser membrane 14 before returning ~ia
tiube 18 to the reaction vessel. ~t the same time the pump
10 circulates a buffer solution through channel 15 segmented
wlth air in channel t6 to the other side of the dialyser
membran~ 14. If an excess of diazo or co~pling component is
present it diffuses through the dialyser membrane 14 from the
sample stream into the buffer solution stream ln direct
proportion to its concent~ation in the sample stream. Thu~
~6~334
as the amount of e.YCess dia~o or coupling component in the
reaction vessel varies during the reaction so the amount
diffusing into the buffer solution varies dlrectly. A
suitable colorimetrlc reagent metered by the `,
proportionating pump 10 in a channel 19 mixes with the buffer
solution carrying the diazo or coupling component e~erging
from the dialyser 13 in channel 15 in a ~ixing coil 20 to form
a c~loured solution, usually a water-soluble azo dyestuff.
The coloured solution passes to the colorimeter 21 where the
air bubbles are removed through -tube 22 to providc a continuous
strea~ which pasces into the flow-through colorimeter cell 23
in which the strength of the coloured solution is contilluously
measured and this is continuousl~ recorded on a chart recorder
Z4.The coloured solution leaves the colorimeter by an effluent
pipe 25 which i5 connected to the proportionating pump 10 to
ensure efficient flow through.
The output signal from the colorimeter is then used to
, control the addition of one or other of the components to the
3 reaction v~ssel by continuously regulating the valves through
which the components are added to the reaction vessel.
The foilowing Examples further illustrate the present
invention.
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33~
EX~L~ 1 -
In the preparation of Colour Index Pigment Yellow 1~
in which a solution of tetrazot;ised 3.3'-dichlorbenzid:ine
is added to a suspension o~ aeetoacetanilide in a stirred
eoupling vessel-at a pH controlled between 4.0 and 6.5
the an~ount of aeetoacetanilicle present in the çouplill~ bath is
'eontinuously monitored by pumping a sample stream from the
reaetor tllrough channel 1l cn the AutoAnalyser to tlle
dialyser 13. A disodium phosphate bu~fer solution is
pumped through channel 15 which picks up acetoacetanilide
~di~fusing through the dialyser membrane 14. I~le buffer
~olution eontaining aeetoaeetanilide is mixed in coil Z0
wlth a solutiorl of tetrazot~sed benzidine-2.2~~disulphonie
aeid addecl through ehannel l9. The yellow dre~tuf~
solution formed passes to the eolorimeter 21 where the
e~ncentration is measured at a wavelength of 410 ~ and
recorded on the recorder 24. An output sig~lal f`rom t71e
reeorder ean be used to regulate the supply of tetrazo
solution to the reaction.
When the eoneentration o~ ace-toaeetanilide present
clrops below a pre-set value on the reeorder the valve
through which the tetrazo solution being added is autolllati~
eally elosed and the presence of excess tetrazo in the
reaction is avoided.
:1 .
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: ~ 9 :~
~06~33~
EX~IPI,E 2
In the preparation of Colour Index Pigment Yellvw 13
a solution of tetrazotised 3.3~-dichlorben~idine and a solution
of acetoacet-2:4-xylidide as its socliurn salt are added simult--
ane,ously to a cou~ g;.vessel at a pH eontrolled throughout
at 4.2-4~5. In order to ensure that a constant srnall excess
of aeetoacet-2:4-~.ylidide is prescnt t:hroughout coupli.ng a
sample stream from t.he coupling vessel is passed through ~he
AutoAnalyser and the ace-toacet-2:4-xylidide which passesthroalgh
the dialysis membrane is picked up in a disodi~n phosphate
solu-tion and is reacted with tetrazotised benzi.cl:Lne-2.2'-Ai-
sulphonic acicl to give a water-soluble yellow clyestuf~ ~lich
i~ measuring on the colorimeter at 410 nm. ~n output sigrlal
from the recorder can be usecl to automatically regulate either
the valve through which the tetrazo solution is being added or
the valve through which the acetoacet~2:4-xylidide solution is
being added so that the e~cess of the coupling component is
maintained at a fixed value throughout the couplirlg and the
pxesence o.f excess tetrazo cornpound is avoided.
,
~_ ' '
. -- .
In the prepa.ration of a recl a~.o pigment lntermediate :.
a solution of diazotised 2:~-di.chloroaniline and a solution :-
of Z-hydroxy-3-naphthoic acid as its sodium salt are addecl
simultaneously to a coupling vessel maintaining the pH at 8.0
throughout.A sampl~ stream from the reaetion i.s passed through
the AaltoAnalyser and the 2 h.ydroxy-3-naphthoic acid which passes .
- 10
" ~L06133~L
throug~ the dialysis membrane is picked up in a water streant
and reacted with acidic ferric chloride solution to gi.ve
a blue coloration measured at 570 nm on the colorimeter.
An output from the recorder is u.sed to regulate the rate of
addition of 2-hydroxy-3-naphthoi.c acid to the reactio~ and
so the excess present throughout can be automatically
controlled at a fi~ed value.
EXAMPLES 4 to 42
Preparation of the water-insoluble azo pignlents
listed in Table 1 can be carried out by controlling the
excess of diaYio component or coupling component in the reaction
medium of the coupling process as required using the
AutoAnalyser in a similar marmer to that described in the
preceding Examples I to 3.
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106~334
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~6~334
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