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Page 1: Direct Dyes and Acid Dyes

Direct Dyes and Acid Dyes

C.V. STEAD

1Cl Ltd Organics Division Hexagon House Blackley Manchester M93 DA

Introduction The period under review, covering from September 1969 to September 1974 has seen changes in the emphasis placed on the various fields of dye research. There has been a marked upsurge in work on acid dyes for nylon and this area is now overshadowed only by reactive and disperse dyes in sheer volume of patent activity. Whilst research on unmetallized dyes for wool has almost vanished, work on metal-complex dyes for this fibre carries on along well-established paths. Direct dyes continue to claim’ a steady, albeit fairly low, amount of attention.

The vast bulk of research has, as always, been directed towards azo compounds and it will be convenient to deal with this first, using it to illustrate the aims of current research before moving on to the other dye classes.

In addition to patents claiming specific dye structures the usual flow of papers outlining particular facets of azo chemistry has continued and, firstly, brief mention should be made of this.

Research on the mechanism of diazotization has included a mathematical treatment of the process [ I ] and a study on the diazotization of aminonaphthol sulphonic acids in sodium acetate solution in the presence of copper sulphate has shown the rate of the second order reaction to be proportional to the heavy metal ion concentration [2]. Base catalysis in the azo coupling of o-diazophenols has been investigated [3] and the structure of the purple colour obtained by the self-coupling of diazotized 1 amino-8-naphthol-3,6-disulphonic acid elucidated as 2,8,8’-trihydroxy-1,1’-azonaphtha1ene-3,6,3’,6‘-tetrasu1- phonic acid [4]. The photochemistry of dyes has been discussed in theoretical terms [5] and interesting results have been published dealing with the fading of azo compounds in solution in the presence of D,L-mandelic acid when a reductive degradation has been shown to occur (6).

Direct Dyes The majority of patents filed relating to direct dyes

concern their application to paper and leather with only minor interest being shown in cotton. There has, however, been one development which has had repercussions in all areas of direct dye application. This has been the fuller recognition of the health hazards associated with the use of the carcinogenic diamine benzidine. For some years now, manufacturers have been at pains to avoid handling this base as such, preferring to deal with a moist salt or even the tetrazotized material. Thus, a recent patent describes the production of tetrazotized benzidine directly by an in siru tetrazotization immediately after rearrangement of hydrazobenzene [7] . However, even

complete avoidance of handling of the diamine in the preparation of dyes is not entirely satisfactory since breakdown of an azo compound in hot aqueous solution can proceed via hydrolysis of the hydrazone form of the dye resulting in regeneration of the parent amine [8]. The possibility is therefore presented of the diamine being reformed from a benzidine-based dye during the dyeing process. The only fully satisfactory solution, now adopted by many dye manufacturers, lies in complete avoidance of the use of benzidine in dye production. This has posed difficult problems, particularly in the case of cheap black direct dyes of the pattern A +. Z + benzidine +. E (e.g. C.I. Direct Black 38) where suitable replacements have had to be found. Much of the work directed towards finding such replacements has involved revival of interest in areas which had been extensively patented many years ago and this effort is, therefore, not immediately apparent from a look at the current patent literature. A few patents have emerged centreing on the pattern cited above but employing in place of benzidine diamines such as 4,4‘-diaminobenzanilides [9] , 1,5-diaminonaphthalenes [ 101 and benzidine-2,2’-disulphonic acid [ 111 as well as dianisidine [ 121 which continues to figure prominently in patent claims. These patents probably represent only a fraction of the research effort which has been expended in the search for replacements for dyes based on benzidine.

Turning to the two major areas of use of direct dyes, namely for the coloration of paper and leather, there is a fairly sharp division of patent activity into claims relating to bright colouring matters of primary hue for the former and drab, tertiary colours for the latter. The bright dyes required for paper coloration are chiefly monoazo compounds in which one of the components is chosen specifically for its ability to confer a high level of substantivity on the dye or, alternatively, fairly simple disazo compounds based on a substantive diamine or twice-coupling component. In the yellow area of the spectrum amines such as 2-(aminopheny1)-benzthiazoles (e.g. I) are favoured for use as diazo components in conjunction with 3-substituted pyrazolones [ 131 , 3-substituted-1- substituted alkyl pyrazolones [ 141 and barbituric acid [ 151 as coupling components. A second favoured type of diazo component incorporates a triazole unit [ 161 and is usually coupled onto an acetoacetarylamide [ 171. Novel coupling components specifically claimed for the production of yellow dyes for paper are acetoacetylaminofluorene sulphonic acids [ 181 . In t h e red area the preferred class of dye results from the coupling of two molecules of a diazotized arylamine with 5,5‘-dihydroxy-2,2’-dinaphthylurea-7,7’-disulphonic acid (11).

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Here the coupling component is responsible for the high level of substantivity. Amines used as diazo component have been 2,Sdisubstituted sulphanilic acids [ 191 and 2-naphthylamine- 6-sulphonic acid [20].

Particular attention has been paid to the details of coupling procedures devised so as to enable these dyes to be prepared in the form of very concentrated aqueous solutions. This is achieved through a coupling designed to produce either the lithium salt [21] or the triethanolamine [22] salt of the sulphonated dye and stable aqueous compositions prepared in this way, containing up to 25% of dye for marketing as liquid form direct dyes are described. Marketing in this form is technically advantageous since it enables automatic metering of the dye into the paper pulp. Orange dyes containing urea linkages [23] prepared by phosgenating aminoazo compounds as well as the disazo violet aniline-2,5-disulphonic acid +

5-alkyl-2-alkoxyaniline + 2-amino-5-naphthol-7-sulphonic acid [24] have also been prepared as concentrated aqueous solutions of their lithium salts. Routine variations, usually for the purpose of improving hues of conventional blue dye structures, have been achieved by coupling tetrazotized dianisidine with one molecule of an aminonaphthol sulphonic acid and one of a naphthol sulphonic acid [25]. Alternatively, two molecules of a naphthol sulphonic acid have been employed as coupling component, the dye then being converted into the copper complex [26].

In contrast to these simple, bright mono- and disazo dyes for paper, the claims relating to direct dyes for leather generally cover more complex structures yielding the tertiary colours usually required for this substrate. A single claim relating to monoazo dyes covers yellow dyes obtained by coupling a diazotized amino phenyl benzthiazole onto an acetoacetarylamide [27]. The remainder of the patents disclosed often use a nitroaminodiphenylamine as diazo component or resorcinol as coupling component to build up polyazo compounds which chiefly provide browns and olives. Thus, brown disazo dyes result from coupling two molecules of diazotized 4-amino-4'-nitrodiphenylamine-2-sulphonic acid onto bis(2-hydroxy-3-carboxyphenyl)methanes [28] or by reducing a 4-(3'-nitrophenylazo)-l-sulphoaryl-5-pyrazolone, diazotizing and coupling onto resorcinol [29]. By varying the final coupling component a variety of other colours can be produced from dyes of this latter pattern [30]. More complex brown polyazo dyes arise by coupling a diazotized 1-aminobenzoylamino-8-naphthol-3,6-disulphonic acid with resorcinol and further coupling the resulting monoazo compound with one or two molecules of a diazonium salt [31]. Olive tetrakisazo dyes of the pattern naphthylamine sulphonic acid + naphthylamine sulphonic acid -+

1 -aminod-naphthol-3,6-disulphonic acid + resorcinol + arylamine [32] provide an illustration of the complexity of structure resorted to in order to obtain drab colours on leather.

Patents relating to metallized dyes for leather often claim a variety of heavy metals complexed with metallizable azo dye structures but the main interest usually lies in the iron complexes which whilst being unimportant on other substrates are particularly suited to the requirements on leather. Metallizable systems claimed cover diazotized o-aminophenols coupled onto pyrazolones [33] or onto previously coupled resorcinols [34] which give brown and olive iron complexes. An interesting patent, [35] describes the preparation of

twice-coppered disazo dyes by an oxidative condensation carried out on simple coppered dihydroxyazo compounds. Thus, treatment of the copper complex of 2-amino-l-naphthol+2-naphthol-3,6-disulphonic acid with hydrogen peroxide leads to the formation of (111 1.

In the application sphere, the loosening effect of additives such as urea on the aggregation of azo dyes has been studied by observations on the change in diffusion current through the solutions [36]. A coacervate system for applying direct dyes to nylon-cotton mixtures [37] and a selection of direct dyes which can be used in conjunction with disperse dyes to colour polyester-cotton blends have been described [38] . Specified aminoalkylsilicones are claimed as aftertreating agents for improving the wash fastness of direct dyes [ 391 .

Acid Azo Dyes Attention has already been drawn to the fact that, within the scope of this review, this is the area of most intensive patenting activity and that this activity is now almost exclusively devoted to supplying dyes for use on nylon. Nylon is dyeable by both disperse and acid dyes, the two classes each having a major strength and a marked weakness. The disperse dyes cover unevenness in the nylon fibre excellently but are somewhat deficient in fastness properties. On the other hand, the acid dyes are capable of giving very good fastness properties but are inferior in dyeing behaviour. This inferiority in dyeing behaviour is the result of irregularities in the substrate caused either by chemical or physical variations along the yarn or differences in degree of crystallinity along the nylon fibre resulting from the application of uneven tension during spinning. The crystalline regions within the fibre are not easily penetrated by many simple acid azo dyes during the dyeing operation and this leads to unlevel dyeing behaviour.

The acid dyes offer the more attractive of the two options available for dyeing nylon and, in the early days, the various dyestuff manufacturers made judicious selections from their available acid wool dyes in order to offer essential ranges of acid dyes for nylon. Rough guide lines became apparent to assist in the selection of dyes which would most effectively overcome the defect of unlevel dyeing. For instance a monosulphonated dye having a molecular weight of about 400-500 or a disulphonated dye with a molecular weight around 800 offers the most likely prospect of level dyeing behaviour. I f the molecular weight is raised above these values unlevel dyeing behaviour ensues whereas if the mokcular weight is lowered the wash fastness properties suffer. Incor- poration of polar substituents as, for example, hydroxyl or acylamino groups generally increases fastness to washing but can also lead to unlevel dyeing behaviour. Within such rough guide lines the finer details of molecular structure come into play to determine which dye structures possess the optimum combination of properties. The patent literature reveals an

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extensive search for these dye structures which has grown markedly over the last few years.

The patent literature of the presently reviewed period ranges over almost all the common classes of azo compounds which are known to give bright and attractive colours. The claims generally outline particular combinations of substi- tuents which have been found effective in optimising dyeing and fastness properties on nylon. Thus, dyes in the greenish- yellow area of the spectrum are obtained by coupling a diazotized sulphonated aniline with either a 1 -phenyl-3-methyl- 5-aminopyrazole [40] or a l-phenyl-3-methyl-5-pyrazolone 14 11 : rigorously defined substitution patterns provide the point of novelty on these well-known structures. Similarly, 2-naphthylamine-1-sulphonic acid has been used in combina- tion with 1-(o-substituted phenyl)-3-methyl-5-pyrazolones (421. 6-Hydroxy-2-pyridones [IV; 431 which have been of considerable interest as coupling components in recent years, have been used in the preparation of dyes varying between greenish-yellow and red [44]. 4Alkylphenols [45] and hydroxy- or alkylamino-pyrimidones [e.g. V; 461 have also been used as coupling components, giving yellows.

i V I

Dyeing of nylon with the novel dye (VI) which is said to condense with the amino groups of the fibre during the dyeing processes to yield a phthalimide-type ring is described [47]. Amines particularly claimed as diazo components for use with a wide variety of coupling components are aminobenzoic acid esters [48] and 2-methoxyaniline-5-sulphonamides [49] .

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Moving to the orange-red area, dialkylanilines have been claimed as coupling components for use with sulphonated diazo components [50] . Alternatively a water-insoluble aminobenzthiazole can be diazotized and coupled with a dialkyl- aniline carrying a single sulphonic acid group in one of the alkyl residues [51] , in which case the hue falls between red and violet. These dyes, are, however not typical of the type of structure generally exploited in this area. Usually coupling components of the naphthalene series are employed since these most readily give the desired colour and fastness properties. Two types of naphthalene compound are impor- tant for this purpose. 2-Hydroxy-3-naphthoic arylamides used in conjunction with anilines containing sulphonic acid [52] or disulphimide [53] groups yield attractive yellowish reds with

generally acceptable levels of light fastness. A markedly higher level of fastness to light is obtained by acid coupling onto 2-amino-8-naphthol-6-sulphonic acid. Using this component a bluish red results. A variety of substituted anilines have been used as diazo components for this purpose; favoured substi- tuents have been trifluoromethyl [54], carboxylic acid ester [55], acylamino [56], sulphone [57] and sulphonamide [58] groups. Aminophthalimides [59] have also been claimed for use in this way, as well as with a wider range of coupling components [60].

These monoazo dyes uniformly display either a single sulphonic acid group or a single disulphimide (-SOz- NH.SOZ-) linkage. In this latter linkage the presence of the two electron-attracting sulphonyl groups joined to the same nitrogen atom makes the proton on the nitrogen atom extremely acidic causing this grouping to be about as effective in solubilising power as the more conventional sulphonic acid group. Again in the disazo series, one disulphimide group is usually sufficient to impart adequate solubility to the dye although assistance is frequently given by a phenolic hydroxyl group. Occasionally, dye structures do incorporate two sul- phonic acid groups. Here again variations in substituents on well-known classes of disazo dyes abound in the patent literature. Thus, aminoazobenzenes diazotized and coupled with phenols and then possibly etherified [61] or tosylated [62] are heavily patented for the production of yellow to orange dyes; besides these usual monosulphonated types, dyes solubilised by the disulphimide grouping [63] are disclosed. Orange to red dyes result when the end-component is an indole derivative [64]. Dyes of the pattern arylamine+l- naphthylamine-t 1 -arylamino-naphthalene carrying one [ 651 or two [66] sulphonic acid groups cover the blue and navy blue areas whilst a wide variety of colour can be obtained using dialkylaniline end components in disazo dye structures [67].

In addition to those claims relating to metal-free azo dyes, copper complexes of both o,o'-dihydroxyazo [68] and the corresponding disazo [69] dyes have figured in the recent literature, giving dyes which are bluish red and navy blue respectively. To achieve adequate solubility in monoazo dyes of this type a sulphonamide group is used to augment the single sulphonic acid group whereas with the coppered-disazo dyes two sulphonic acid groups are generally desirable. Metal complexes of dyes obtained by coupling either a diazotized 8-aminoquinoline-5-sulphonic acid [70] or an o-aminophenol [71] onto a 2,3-dihydroxy-5-halogenopyridine are a rather more novel type described for the dyeing of nylon.

Metal Complex Dyes for Wool While interest in metal-free non-reactive azo dyes for wool has virtually disappeared, work on metal-complex dyes carries on steadily along well-established lines. Of more interest than the fairly routine structural variations disclosed in the patent literature are the contributions to the basic understanding of the chemistry of these compounds which have shown impressive advances in recent years. A close study of the role of the dye as a tridentate ligand, displacing other ligands (usually water or ammonia) from around the metal ion during complex formation, has enabled improved methods of com- plex formation to be evolved and, in particular, has allowed the ready preparation of pure mixed cobalt complexes. This work which has been reviewed previously [72] is now phasing out through the patent literature [73]. An interesting point

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with regard to cobalt complex formation is that the formation usually starts with a solution of a cobaltous salt and during metallization a change in the valency state of the heavy metal ion occurs leading to a cobaltic complex. This change in valency is accomplished by an oxidation process which occurs at the expense of a portion of the dye being metallized, thus placing a limit on the yield of dye which can be obtained from this process. Addition of 3-nitrobenzenesulphonic acid to the reaction mixture supplies a mild oxidising agent which prevents such destruction of the dye thus allowing quantitative yields of the 1:2 cobalt complexes to be obtained [74]. Detailed structural studies of chromium complexes of azo compounds which involve amino groups located ortho to the azo linkage in complex formation show that a proton is not invariably lost from the amino group [75] when the metal complex is formed. A novel pentacyclic cobalt complex formed from a bis-o-hydroxyazo dye is described. [76].

The complexes disclosed in the patent literature almost exclusively are of the mixed type i.e. where the two metallizable azo structures coordinated to the metal atom are dissimilar. Whilst a small number of patents claim dyes devoid of sulphonic acid groups [77] the majority contain a single sulphonic acid group located in one of the metallizable dye units [78], these being designed to be of a sufficiently high molecular weight to ensure that this acid group does not lead to an excessively polar character and, hence, skittery dyeing behaviour. Occasionally this is accomplished by making one of the dye units a disazo structure [79]. Heterogenous cobalt complexes, prepared by cobalting mixtures of azo dyes are still found of interest [80]: Mention is also made of the use of 1:2 chromium complexes containing a single sulphonic acid group in the mass coloration of nylon [ 8 1 ] . Food Dyes A few patents continue to appear relating to dyes for use in the coloration of food, making this area, which is often neglected in reviews, worth a cursory mention. It is, of course, of paramount importance that a dye for this purpose should be completely non-toxic. Patents relating to these dyes usually emanate from the USA and the criterion for non-toxicity which they use is the ability to pass regulations laid down by the United States Government’s Food and Drug Administra- tion. The dyes claimed are generally simple sulphonated monoazo dyes, usually red in colour. Examples are 5-alkyl-2- alkoxyaniline-4-sulphonic acids diazotized and coupled with 2-naphthol-6-sulphonic acid [ 821 , 4-alkoxyaniline-3-sulphonic acids similarly combined with 1-naphthol disulphonic acids [83] and sulphanilic acid+1-acetylamino-8-naphthol-3,6- disulphonic acid [84]. In these dyes it is noteworthy that every component used is sulphonated to ensure water-solu- bility of potential break-down products. In addition to the non-toxic requirement, other desirable properties are resistance to decolorization by sulphur dioxide, retention-of hue over a range of pH values and stability to heat, all of which are dictated by their end use.

Anthraquinone Dyes A reasonably large number of patents relating to sulphonated anthraquinone dyes have been published. The dyes disclosed are occasionally claimed for use on wool but far more often their application to nylon is stressed. The main driving force for research in this area is, as in the azo series, the desire to

capture a greater share of the expanding market for nylon dyes by supplying dyes of improved performance on this fibre. The majority, although not all, of the dyes described are bright reddish blues, this being the area in which the anthrdquinorie chromogen is pre-eminent in giving clarity of hue coupled with the possibility of excellent light fastness.

The patents appearing may be subdivided into two main groups, depending upon whether the dye preparations start f rom 1 -ami n o-4-b r omoanthraquinone-2-sulphonic acid (bromamine acid) or from a 1,4-dihydroxyanthraquinone. In the first of these groups the dye is prepared by condensation of bromamine acid with a suitable amine, the choice of which determines the properties of the dye. The resultant dye is a 1-amino-4-substituted aminoanthraquinone-2-sulphonic acid. If the selected amine is an alkylamine, leading to a 4-alkyl- amino-anthraquinone derivative, the colour is particularly brilliant but the light fastness is often only moderate. Conversely, an arylamine, giving a 4-arylaminoanthraquinone. generally leads to excellent light fastness but the colour is less bright. Patents appearing in this area disclose claims for amines designed to achieve the optimum balance of these two properties. Alkylamines are less frequently chosen; those disclosed are often complex [85], as, for example, I-amino- 3,5,5-irimethylcyclohexane [86] , which is used in the prepara- tion of dye VII.

In the more commonly used arylamines substituents located in the 2,6- positions as, for example, in the dye (VIII) enhance the brilliance of colour and the solubility by twisting the pendant phenyl ring out of the plane of the anthraquinonc nucleus [87] . Electron-attracting substituents located in the pendant ring are also sometimes beneficial. This is exploited by locating a sulphonamide [88] or disulphimide [89] grouping on the phenyl nucleus, this also serving to improve the solubility. Rather more complex dyes are built up by condensation of bromamine acid with an aminophenol and subsequent condensation of the hydroxyl group in the intermediate dye with 3-chlorosulphonylbenzoic acid [90] , or condensation of bromamine acid with an aminobenzthiazole [91] or an aminoazo compound [92].

The second main group of patents use 1,4-dihydroxy- anthraquinone as a starting material; this is initially condensed with two molecules of an amine leading to a 1,4-di-(substi- tuted amino) anthraquinone. This is then sulphonated or sulphated to give an acid dye. Both alkylamines [93] and 2,Qdisubstituted arylamines [94] are used in the synthesis of these dyes; occasionally one of the substituted amino groupings carries an alkyl group and the other an aryl group [95] . Whilst the combinations of substituents mentioned above give blue dyes, the location of two simple arylamine residues which do not bear 2,6-oriented substituents on the anthraquinone nucleus allows both pendant phenyl rings to conjugate with the anthraquinone nucleus leading to a green dye. Thus, sulphonation of 1 ,4-di-p-toluidino-anthraquinone

4 REV. PROG. COLORATION VOL. 6 1975

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leads to dyes giving greens on nylon [96] . In addition to these dyes limited interest has been

displayed in sulphonated 1-amino4hydroxyanthraquinones carrying either an aryloxy- [97] or aryloxyalkoxy- [98] substituent in the 2-position. Such dyes (e.g. IX) give bright reds on wool and nylon.

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Other Classes of Dyes In addition to the major interest shown in the azo and anthraquinone dyes the patent literature can invariably be relied upon to produce a smattering of claims relating to other dye types. Thus, in the extensively worked copper phthalo- cyanine field methods for the production of sulphonated material containing a proportion of the 4sulphonic acid isomer, rather than the 3-isomer, are detailed [99]. Blue dyes prepared by sulphation of copper phthalocyanine sulphon-/3- hydroxyethylamide are also described [ 1001 and condensation of copper phthalocyanine tetrasulphonchloride with a diamino benzene sulphonic acid followed by diazotization and coupling with a pyrazolone has been used in the preparation of green dyes for leather [ 1011.

Yellowish brown nitro dyes prepared by condensing an aminodiphenylamine with a 2-nitrochlorobenzene, carrying a further electron-attracting substituent in the 4- position, have attracted some interest as dyes for nylon [102]. The use of blue triphendioxazine dyes, well known as direct dyes for cotton, has also been extended to nylon [ 1031. An attempt to supply fluorescent dyes for the coloration of this fibre is apparent from the patent literature. The dye types investigated have been heterocyclic dyes, chiefly of the coumarin type [ 1041 typical of which is the dye (X). Dyes based on the novel ring system (XI) are also claimed for this purpose [ 1051 ; both dye types give mainly yellow.

Future Prospects Any assessment of future prospects is, of necessity, subjective, invariably representing the author’s personal view of the current situation. I t must be stressed that these comments are no exception.

Dramatic changes rarely occur, continual shifts in emphasis being responsible for altering the direction of future progress. At present, emphasis is altering to cope with additional criteria which will become increasingly important in deciding the success or otherwise of dyes, These are the availability of intermediates, the reduction of pollution and a low consumption of energy and water. In the direct dye field the first of these criteria has already had some impact and the second weighs heavily against after-coppered direct dyes. The last two would appear to encourage continuous dyeing techniques for which direct dyes are generally unsuitable. This accumulation of factors should ensure further progressive encroachment of reactive dyes into territory previously dominated by direct dyes.

Research on wool dyes has now probably dwindled to a steady level and very little change can be expected. The continuing growth of nylon usage should, however, ensure the continuance of work directed against specific targets although the absence of any major defects in the available dyes makes any major advance unlikely.

If any marked advance is to be seen in the near future, the impression is formed that the frontier between reactive dyes and direct dyes is the area most ripe for change.

References 13. 1.

2.

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Sidorov, Passett and Kalle, Zhur. priklad khim., 42 (1969) 2545. Kozlov and Volodarskii, Zhur. obschch khim., 39 (1969) 325. Jemini, Kaller and Zollinger, Helv. chim. Acta, 53 (1970) 72. Stead, J.C.S. C. Organic (1970) 693. Egerton and Morgan, J.S.D.C. 86 (1970) 79. Van Beck, Heertjis, Houtepen and Retzloff, J.S.D.C., 87 (1971) 87; van Beck, Heertjis and Schaafsma, J.S.DK., 87 (1971) 342; van Beck, Heertjis and Rutges, J.S.D.C., 89 (1973) 389. Columbian Carbon Co., B.P. 1,239,273 (1967). Mel’nikov and Kirillova, Zhur. priklad khim.,42 (1969) 2566. BAY, BP 1,327,914(1971). Idem, BP 1,371,877 (1972). Idem, BP 1,371,975 (1971), Idem, BP 1,349,611 (1971).

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62.

63. 64.

Ugine Kuhlmann, BP 1,217,819 (1968). S, BP 1,257,581 (1969). Fran, BP 1,267,937 (1968). Ugine Kuhlmann, BP 1,180,781 (1967). FH, BP 1,238,780 (1968); S, BP 1,306,836 (1969); BP 1,3 10,825 (1969); Ugine Kuhlmann, BP 1,230,948 (1968). BAY, BP 1,341,646 (1971). CCY, BP 1,325,507 (1970); GAF, USP 3,423,393 (1966). S, BP 1,306,527 (1969); BP 1,313,382 (1969). BASF, BP 1,327,965 (1970). Malik and Saleem, J. Oil Col. Chem. Assocn.,52 (1969) 551. Demidova, Ershov and Kharkharov, Tr. Probl. Lab., Leningrad. Inst. Tekst. Prom.. No. 13 (1971) 332 (Chem. Abs., 78 (1973) 73486). Kewanee Oil Co., USP 3,738,800 (1972). Union Carbide Corpn., USP 3,741,721 (1965). DUP, BP 1,349,112 (1971). Idem, USP 3,563,685 (1967); FH, BP 1,184,703 (1967); BP 1,285,487 (1969); ICI, BP 1,169,005 (1967); BP 1,175,666 (1967); MAC, USP 3,655,640 (1969); S, BP 1,302,776 (1969). Crompton and Knowles Corpn., BP 1,239,548 (1969). ICI, BP 1,263,268 (1968); BP 1,351,383 (1971). BASF, BP 1,346,817 (1970); ICI, BP 1,331,261 (1970); BP 1,331,445 (1970). BAY, BP 1,246,783 (1968);BP 1,331,415 (1971). BAY, BP 1,217,272 (1967);BP 1,223,489 (1967). Gritchenko and Kalontarov, Zhur. priklad Khim., 45 (1972) 2772. BAY, BP 1,269,887 (1969). Toms River Chemical Corpn., USP 3,600,377 (1968). BAY, BP 1,325,147 (1970); BP 1,326,171 (1971); DUP, USP 3,657,220 (1969). BAY, BP 1,265,283 (1969). FH, BP 1,199,424 (1966); BP 1,264,391 (1968). Crompton and Knowles Corpn., BP 1,272,307 (1968). BAY, BP 1,229,356 (1968). BASF, BP 1,238,924 (1967); GAF, USP 3,511,829 (1967); S, BP 1,350,256 (1970). BAY, BP 1,246,766 (1969); BP 1,267,484 (1969); S, BP 1,223,269 (1967). FH, BP 1,271,301 (1968). CGY, BP 1,332,914(1969); ICI, BP 1,325,541 (1969); 1,325,542 (1969). BASF, BP 1,205,176(1967). Idem, BP 1,213,396 (1967); BP 1,272,819 (1968). BAY, BP 1,258,219 (1969); BP 1,281,277 (1969);BP 1,281,989 (1969); BP 1,297,214 (1970); BP 1,339,381 (1971); CGY, BP 1,330,383 (1970); BP 1,336,935 (1970); Compton and Knowles Corpn., BP 1,268,702 (1968); DUP, USP 3,485,814 (1965); 3,676,050 (1969); S, BP 1,201,546 (1967); Toms River Chemical Corpn., BP 1,285,045 (1968). Toms River Chemical Corpn., BP 1,276,698 (1968); USP 3,594,363 (1968); USP 3,637,338 (1970). BAY, BP 1,264,071 (1969). Idem., BP 1,328,774 (1971); BP 1,333,522 (1971); BP 1,342,195 (1971); BP 1,342,197 (1971).

65.

66. 67.

68. 69.

7 0. 71. 72. 73. 74. 75. 76. 77.

78.

79.

80. 81. 82.

83. 84. 85. 86. 87. 88. 89. 90.

91. 92. 93. 94. 95.

96. 97.

98. 99.

100. 101. 102.

103. 104.

105.

Idem, BP, 1,265,428 (1969); Crompton and Knowles Corpn., BP 1,251,460 (1969); USP 3,814,749 (1971). ICI, BP 1,322,704 (1969); BP 1,322,705. BAY, BP 1,243,941 (1969); BP 1,298,280 (1969): BP 1,300,366 (1970);BP l,309,919(1970);BP 1,316,724 (1970); CKC, BP 1,289,856 (1968); Crompton and Knowles Corpn., USP 3,580,901 (1968); FH, BP 1,198,886 (1967); Fran, BP 1,272,884 (1969); Toms River Chemical Corpn., BP 1,338,883 (1971). Crompton and Knowles Corpn., BP 1,205,529 (1968). BAY, BP 1,330,227 (1971); CKC, BP 1,299,033 (1970). CGY, BP 1,340,270 (1970). Idem, BP 1,343,641(1970). Stead, Rev. Prog. Color., 1 (1969) 23. ICI, USP 3,356,671 (1965). CGY, BP 1,264,872 (1968). Schetty, Helv. Chim. Acta, 52 (1969) 1796. Idem, ibid, 52 (1969) 1806. BAY, BP 1,162,084 (1967); CGY, BP 1,311,682 (1969); ICI, BP 1,163,713 (1967). CGY, BP 1,248,484(1965);BP 1,318,067 (1969); Gy, BP 1,197,265 (1967); BP 1,201,560 (1967); USP 3,459,727 (1966);ICI BP, 1,200,181 (1966);KYK,BP 1,347,460 (1971). Ugine Kuhlmann, BP 1,178,485 (1966); BP 1,196,552 (1967) BP 1,224,424(1968). FH, BP 1,330,136 (1969); Gy, BP 1,164,525 (1966), USP 3,359,253 (1967); USP 3,374,219 (1967). S, BP, 1,163,126 (1966). CGY, BP 1,266,674 (1 969). Allied Chemical Corpn., BP 1,164,249 (1966); USP 3,519,617 (1967); USP 3,640,733 (1969). Idem, BP 1,224,513 (1967). Unilever, BP 1,270,656 (1968). BASF, BP l,169,154(1966);BP 1,177,682 (1966). S, BP 1,243,457 (1969). Idem, BP 1,161,941 (1966). Idem, BP 1,167,664 (1966). CGY, BP 1,277,439 (1968). Crompton and Knowles Corpn., USP 331 3,402 (1971). BAY, BP 1,296,3 19 (1 970). FH, BP 1,295,772 (1970). S,BP 1,210,891 (1967);BP 1,218,399(1967). Gy , USP 3,s 19,656 (1967). BAY, BP 1,311,916 (1969). ICI, BP 1,166,998 (1966). S, BP 1,176,626 (1966). BASF, BP 1,273,675 (1969). BAY, BP 1,245,037 (1968); Crompton and Knowles Corpn., USP 3,627,473 (1965). BAY, BP 1,264,280 (1969). S, BP 1,280,056 (1969). CGY,BP 1,241,240 (1968). Ugine Kuhlmann, BP 1,220,143 (1967). CGY, BP 1,343,102 (1971); FH, BP 1,290,319 (1969); S, BP 1,311,702 (1969); BP 1,347,897 (1970). ICI, BP 1,353,604 (1970). BASF, BP 1,275,778 (1968); BP 1,341,267 (1970); BAY, BP 1,329,043. CGY, USP 3,720,671 (1970).

6 REV. PROG. COLORATION VOL. 6 1975