Color Pigments - ACS Symposium Series (ACS Publications)

53 Color Pigments 1

2

LAWRENCE R. LERNER and MAX SALTZMAN 1

Dyes and Pigments Division, Mobay Chemical Corporation, Hawthorne, ΝJ 07507 Institute of Geophysics and Planetary Physics, University of California, Los Angeles,CA90024

Downloaded by NORTH CAROLINA STATE UNIV on November 8, 2013 | http://pubs.acs.org Publication Date: September 25, 1985 | doi: 10.1021/bk-1985-0285.ch053

2

Inorganic Pigments Chrome Pigments Iron Oxide Pigments Cadmium/Mercury Sulfides Colored Titanium Oxides Organic Pigments Phthalocyanines Quinacridones Vat Pigments Isoindoline Pigments Azo Pigments Miscellaneous Due to the many developments that have occurred in the pigment field since the 1920s, proper treatment of a l l important topics is simply not possible in a single chapter. We, therefore, will emphasize the major developments since the end of World War II. Within this period we will cover inorganic pigments somewhat more briefly than the organic pigments due to the greater complexity of the latter field, combined with space limitations and the greater experience of the authors in the organic pigment area. As only an overview can be provided, the reader is encouraged to seek more complete and detailed information in the papers of Gaertner (1), Heinle (2), Hopmeier (3), Inman (4), Kehrer (5), and Lenoir (6) and books by Zollinger (7) and Lubs (8). We are fortunate that in 1973 an outstanding treatise on the entire field of pigments was published, entitled "Pigment Handbook" by Patton (9), which in its three volumes provides a wealth of information to anyone interested in pigments for any field of application. The development of new coating resins, p l a s t i c s , and synthetic f i b e r s , as w e l l as new methods of u t i l i z a t i o n o f a l l o f these m a t e r i a l s , has c r e a t e d an unprecedented demand f o r m a t e r i a l s t o impart c o l o r to these otherwise c o l o r l e s s substances. Not only i s i t necessary t o c o l o r these p l a s t i c s and r e s i n s but a l s o i t i s 0097-6156/ 85/0285-1271 $07.25/0 © 1985 American Chemical Society

In Applied Polymer Science; Tess, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.


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APPLIED POLYMER SCIENCE

important t h a t t h i s c o l o r a t i o n stand up f o r some time i n s p i t e of exposure to a h o s t i l e environment. Many new resins are d i f f i c u l t to pigment and r e q u i r e both h i g h - e n e r g y i n p u t and f a i r l y h i g h temperatures. Any colorant f o r such a system must be r e s i s t a n t to both the p h y s i c a l and c h e m i c a l s t r e s s e s encountered i n the dispersion conditions and i n the f i n a l a p p l i c a t i o n methods. To begin, l e t us look at the requirements for a c o l o r pigment to s a t i s f y the demands of modern industry. The f o l l o w i n g i s a l i s t of d e s i r a b l e pigment p r o p e r t i e s : high chroma; f a s t n e s s to l i g h t , weather, migration, and s o l v e n t s ; resistance to processing chemicals and heat. The f i r s t requirement, that of high chroma, i s necessary to g i v e b r i g h t , c l e a n s e l f c o l o r s , both i n f u l l tone and i n d i l u t i o n w i t h white pigments or a mixture with nearly c o l o r l e s s p l a s t i c s . This h i g h c h r o m a t i c i t y a l s o permits b l e n d i n g w i t h other c o l o r a n t s to obtain mixtures without s u b s t a n t i a l l o s s of c l e a n l i n e s s . Fastness to l i g h t , both i n f u l l shade and when d i l u t e d w i t h white, permits the use of a pigment under c o n d i t i o n s of l o n g times of exposure so that r e f i n i s h i n g w i l l not be necessary for the e f f e c t i v e l i f e of the object being colored or i n the case of i n t e r i o r house paint (or even e x t e r i o r house paint) u n t i l the homemaker gets t i r e d of the c o l o r . Fastness to weathering i s important f o r automotive, a r c h i t e c t u r a l , and engineering coatings, which are exposed to a l l kinds of weather, i n c l u d i n g the i n d u s t r i a l environment. The m u l t i t u d e of c o l o r s o b t a i n a b l e i n a u t o m o b i l e s today i s w i t n e s s to the success of the pigment i n d u s t r y i n s u p p l y i n g the necessary c o l o r pigments to p r o v i d e any c o l o r t h a t i s d e s i r e d — i n c l u d i n g b l a c k ! Fastness to m i g r a t i o n permits the use of a pigment i n a p l a s t i c f i l m or a c o a t i n g t h a t i s to be i n c o n t a c t w i t h other o r g a n i c m a t e r i a l s , i n c l u d i n g the seat of one's s y n t h e t i c f i b e r c l o t h i n g or w i t h bare skin. Fastness to s o l v e n t s i s necessary f o r a l l paint systems where one c o l o r i s to be sprayed over another, and i t i s a l s o important f o r the s t a b i l i t y of any p a i n t f o r m u l a t i o n c o n t a i n i n g s o l v e n t s . Fastness to heat i s needed f o r those materials to be used i n today's high-bake f i n i s h e s as w e l l as those to be incorporated i n t o p l a s t i c s t h a t are processed at h i g h temperatures such as p o l y p r o p y l e n e . Resistance to chemicals i s almost s e l f - e v i d e n t i n that a l l pigments are chemical e n t i t i e s that are not t r u l y i n e r t ; therefore, they must react i n the systems i n which they are employed. For the sake of b r e v i t y , we have r e f e r r e d to the f a s t n e s s of a pigment. I t should be understood that the fastness of the pigment powder by i t s e l f has no r e a l s i g n i f i c a n c e . The o n l y f a s t n e s s properties that are of any value are those of the complete pigmented system. By t h i s i s meant the pigment incorporated i n the coating or r e s i n i n which i t i s to be employed under the exact c o n d i t i o n s of incorporation and under the exact condition of use. This makes i t d i f f i c u l t to pass g l o b a l judgments as to the u s e f u l n e s s of a pigment, but i t has been shown i n studies such as those of Smith and Stead (10), Vesce (11, 12), and L e v i s o n (13) that t h i s concept of fastness i s the only v a l i d one. Inorganic Pigments The inorganic pigments used today include many of those known since e a r l i e s t times, such as i r o n oxides and mercuric s u l f i d e or


53.

LERNER AND SALTZMAN

Color Pigments

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v e r r a i l l i o n . The inorganic pigments are the "workhorse" pigments of the i n d u s t r y and are the b a s i s f o r the m a j o r i t y of the c o l o r e d f i n i s h e s today. Improvements on these o l d e r types accounts f o r many of the inorganic pigments i n use today. Chrome Pigments. Chrome pigments based on lead chrornate and mixed l e a d molybdenum s a l t s have been the b a s i s f o r y e l l o w and orange pigments since t h e i r discovery i n the 19th century. The lead chromate yellows are based on s o l i d s o l u t i o n s of lead chromate (PbCrC^) and lead s u l f a t e (PbS04>. The higher the amount of PDSO4, the l i g h t e r the yellow. The s o - c a l l e d molybdate oranges are s o l i d s o l u t i o n s containing perhaps 75% lead chromate (PbCr04) with the rest made up with lead molybdate (PDM0O4) and lead s u l f a t e (PbS04). The p r i n c i p a l defect of chrome pigments i s t h e i r tendency t o darken on exposure. Developments i n the 1940s l e d to the introduction of "predarkened" pigments i n the e a r l y 1950s. Treatment of the precipitated pigments w i t h f o r e i g n m e t a l s such as antimony, bismuth, or v a r i o u s r a r e earths lead to d u l l e r c o l o r s but improved l i g h t fastness. I t was l a t e r found t h a t e n c a p s u l a t i o n of the pigment c r y s t a l l i t e w i t h a "skin" of s i l i c a provides a p r o t e c t i v e b a r r i e r that aids chemical r e s i s t a n c e ( p a r t i c u l a r l y a g a i n s t s u l f u r d i o x i d e ) and h e a t resistance. Various s i l i c a coated chrome pigments are a v a i l a b l e today. The most severe blow to the continued use of chrome pigments has come from the proponents of s a f e t y i n banning the use of even i n s o l u b l e l e a d pigments i n any p a i n t t h a t might be approached by c h i l d r e n . However, even w i t h o u t l e g i s l a t i v e requirements, many automotive and other i n d u s t r i a l f i n i s h e s are being f o r m u l a t e d without chrome c o l o r s . Iron Oxide Pigments. The discovery of i r o n oxide pigments i s l o s t i n antiquity. The cave paintings of e a r l y man were made with earth c o l o r s composed of iron oxides. Even today, natural i r o n oxides are s t i l l i n use. The yellows such as the y e l l o w ochers and siennas are hydrated f e r r i c o x i d e s (Fe203 H20). The nonhydrated f e r r i c oxides (Fe203) comprise the reds and browns such as the red ochers and brown umbers. The blacks are mixed ferrous and f e r r i c oxides (Fe304 or more p r e c i s e l y FeO»Fe203). During t h i s century, p r o c e s s e s were d e v e l o p e d t o produce synthetic iron oxides covering the e n t i r e c o l o r range of the natural c o l o r s . These s y n t h e t i c i r o n o x i d e s had the advantage of g r e a t e r p u r i t y and better p a r t i c l e s i z e d i s t r i b u t i o n , l e a d i n g t o c l e a n e r , stronger pigments. In recent years, demand f o r low-cost transparent pigments has l e d t o very f i n e p a r t i c l e s i z e d i r o n o x i d e s t h a t , though c h e m i c a l l y i d e n t i c a l w i t h the p r e v i o u s l y developed opaque types, have the high transparency needed, p a r t i c u l a r l y i n m e t a l l i c automotive f i n i s h e s . e

Cadmium/Mercury S u l f i d e s . One of the major accomplishments of the past 25 years has been the i n t r o d u c t i o n of a s e r i e s of red and maroon pigments based on mercury and cadmium s u l f i d e s (CdS»xHgS), to r e p l a c e the well-known cadmium s u l f o s e l e n i d e s . The work was prompted by the i n c r e a s i n g shortage of s e l e n i u m and i t s e v e r increasing price. In t h e i r search f o r replacement f o r the standard


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cadmium pigments, workers at Imperial Color and Chemical (now a division of Ciba-Geigy) successfully substituted mercury for selenium to produce the mercadium pigments. While they are not as heat r e s i s t a n t as the cadmium sulfoselenides, they are quite s a t i s f a c t o r y for many uses. The hue range varies from orange to maroon as the weight percent of CdS decreases from approximately 90% to 74%. Colored Titanium Oxides. Modification of titanium dioxide i n which n i c k e l and antimony are incorporated into the c r y s t a l l a t t i c e has given a series of weak yellow pigments ranging i n hue from a clean almost lemon yellow to a buff. These are quite durable and have the a d d i t i o n a l advantage of being s e l f - c h a l k i n g so that on weathering, the o r i g i n a l color i s not masked by a white chalk which can be the case when the color i s based on s t r a i g h t titanium white modified with a t i n t of organic colorant. Other colored oxides such as those based on cobalt and aluminum have been used to a l i m i t e d extent, especially for high-temperature applications. An additional i n t e r e s t i n g use of T1O2 was developed i n the 1960s whereby mica i s coated with a controlled thickness of T1O2 to produce colored pigments that derive t h e i r color from l i g h t interference phenomena. Introduction of small amounts of a colored material such as Fe2Û3 allows color both from interference and absorption. These pigments f i n d use i n both cosmetic and i n d u s t r i a l markets because of t h e i r m e t a l l i c iridescent l u s t e r . Organic Pigments Phthalocyanines. The modern era of synthetic organic pigments i s generally considered to have begun with the discovery and subsequent marketing of copper phthalocyanine pigments i n 1935 by Imperial Chemical Industries. Even today, the pigmentary form of t h i s material i s considered the standard by which a l l other pigments are judged. Scheme I shows the synthesis of copper phthalocyanine (14) from phthalic anhydride and urea i n the presence of copper. Most of the commercially a v a i l a b l e pigments of the phthalocyanine class are made from the copper compound or i t s halogenated d e r i v a t i v e s . The most widely used are the two c r y s t a l forms of the same chemical composition; the reddish blue alpha phase and the greenish blue beta phase of copper phthalocyanine, Pigment Blue 15 (I). Metalfree phthalocyanine ( I I ) , Pigment Blue 16 (15), i s a greenish blue pigment that can be produced by f i r s t preparing a phthalocyanine containing a l a b i l e metal such as magnesium or calcium and then removing the metal by acid treatment. Although the chemical syntheses of phthalocyanines i s r e l a t i v e l y simple, the preparation of the pigmentary form requires much ingenuity. I t i s probable that more work has been done on the " f i n i s h i n g " or "conditioning" of phthalocyanines than on the synthetic methods. Physical and chemical treatment to control p a r t i c l e size and shape, c r y s t a l habit, and rheological properties of the pigments includes a c i d pasting, s a l t - g r i n d i n g , and solvent treatments. The admixture of small amounts of substituted phthalocyanines has also been used to improve the working properties such as resistance to f l o c c u l a t i o n and s t a b i l i t y to solvents.



53.

LERNER AND SALTZMAN

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Color Pigments

ι P.B. 15

Scheme I . Copper phthalocyanine synthesis.

Y

Y

X-Cl Y=Br ;



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The only other major class of pigmentary phthalocyanines, phthalocyanine greens, are made by the halogenation of the copper compound with either chlorine, bromine, or a mixture of both. Approximately 14 positions are occupied by the halogen. In the case of Pigment Green 7 ( I I I ) , they are a l l chlorine, which gives a blue shade of green. Increasing s u b s t i t u t i o n of bromine for c h l o r i n e to a t o t a l of approximately eight or nine bromine atoms gives increasingly yellow shades of green of which the most yellow i s Pigment Green 36 (IV). We pass on from these pigments not because they are unimportant but because they are so superior to pigments of almost any other chemical class that we must search through a very large number of other chemical types to find colors whose pigment properties equal those of the blue and green phthalocyanines. Quinacridones. Much e f f o r t was expended to carry the hue of phthalocyanines i n the other d i r e c t i o n to produce reds and v i o l e t s with outstanding fastness properties, but these e f f o r t s proved to be unsuccessful. However, i n the 1950s a number of developments d i d take place with other chromophores i n t h i s color range to produce new lines of outstanding pigments. The development and commercialization of quinacridone pigments by Du Pont was one of these developments. Though the synthesis of quinacridone was f i r s t reported i n 1935 (16, 17), i t was o r i g i n a l l y evaluated as a p o t e n t i a l vat dye and found to be of no i n t e r e s t . However, beginning i n the l a t e 1950s, patents issued to Du Pont (18) described processes for making three c r y s t a l forms of l i n e a r trans-quinacridone i n pigmentary form. These forms are the red, alpha (a) and gamma ( γ ) , and the v i o l e t , beta (0). Scheme I I outlines the process described i n the Du Pont patents. The process actually starts with dianilinodihydroterephthalic ester ( V I I ) , which can be made by the condensation of succinic acid ester to c y c l i c succinyl succinate (VI) (Step 1), followed by condensation with a n i l i n e (Step 2). This intermediate (VII) i s then ring closed at high temperature to form dihydroquinacridone (VIII) (Step 3 ) , which i s oxidized under controlled conditions to a crude alpha, beta, or gamma c r y s t a l form of quinacridone (IX) (Step 4). These crudes are then conditioned to the finished pigment. Scheme I I I describes another route that was patented by Harmon Colors (19-21) also s t a r t i n g with dihydroterephthalic ester ( V I I ) , but the ester i s oxidized and hydrolyzed f i r s t to (X) and then r i n g closed i n polyphosphoric acid to IX. Controlled drowning of the acid melt onto various solvents gives the finished pigment d i r e c t l y . A t h i r d route developed by Sandoz (22) shown i n Scheme IV allows one to make unsymmetrically substituted quinacridones by stepwise condensation (Steps 1 and 2) of the two amines c a r r i e d out under c a r e f u l l y controlled conditions (23). The v i o l e t quinacridone (beta form) has found much use i n the past i n admixture with molybdate orange to make bright " f i r e engine" reds. With many paint manufacturers removing t h i s lead-based orange from use, a large p a r t i c l e sized opaque -quinacridone red i s now being substituted i n many cases for the v i o l e t , orange combination in industrial finishes. Stronger, more transparent forms of both the alpha and gamma red forms are sold for use i n paints and


53.

LERNER A N D SALTZMAN

STEP 1.

mi

Color Pigments

CYCLIZATJON co R 2

C0 R 2

OH".

RO,C

,C0 R


2

R0 C

V

2

STEP 2.

CONDENSATION

Z

RO-C

VI

2

STEP 3.

Η

VII

RING CLOSURE

.ÎL^C0 R

©r X O 2

R0 C 2

VII

©OX© 8

Ν

VIII Η

STEP Η. OXIDATION

Scheme I I . Quinacridone v i a dihydroquinacridone.

OXIDATION - HYDROLYSIS

Κ

- "2η

VII

Η

RIN6 CLOSURE Η

•

2

χ

Η

H

ο

"

Scheme I I I . Quinacridone v i a polyphosphoric acid r i n g closure.



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plastics. Other c r y s t a l forms of quinacridone have been reported but seem to be either special modifications, more c r y s t a l l i n e forms, or mixes of the alpha, beta, and gamma types. Two substituted quinacridones have been introduced commercially and f i n d use: 2,9-dimethylquinacridone, Pigment Red 122 ( X I ) , and 2,9-dichloroquinacridone, Pigment Red 202 (XII). Both are magenta i n shade. I n t e r e s t i n g l y , the substituents are not ortho to either the carbonyl oxygens or the NH groups. I t has been found that orthosubstituted quinacridones have poorer weatherfastness. Apparently ortho substituents i n t e r f e r e with intermolecular hydrogen bonding. I t i s t h i s hydrogen bonding (Figure 1) that seems to account for the outstanding s t a b i l i t y and i n s o l u b i l i t y of quinacridone, which has a molecular weight of only 312 (24-26). Other chemical forms of quinacridone are known but are not as outstanding i n t h e i r properties. For example, l i n e a r cis-quinacridone (XIII) (27) and epindolidione (XIV) (28, 29) are both yellows with i n s u f f i c i e n t weatherfastness for commercial use, A t h i r d yellow d e r i v a t i v e , quinacridonequinone\ (XV), made as shown i n Scheme V or d i r e c t l y from the oxidation of quinacridone, i s also not weatherfast by i t s e l f . However, chemists at Du Pont found that s o l i d solutions of the quinone with quinacridone leads to pigments with improved fastness properties (30-32). Today a maroon containing about 60% quinacridone and 40% quinacridonequinone and a gold containing about 75% quinacridonequinone are sold commercially. S o l i d solutions can also be prepared between variously substituted l i n e a r trans-quinacridones, and a s c a r l e t containing a mixture of approximately 60% quinacridone and 40% 4,11-dichloroquinacridone (an orange) i s also on the market. Vat Pigments. Another chemical class of compounds that has been exploited to produce pigments i n the same hue area as quinacridones are the thioindigos. Thioindigos are members of a group of compounds referred to as "vat pigments," which are pigments based on t e x t i l e vat dyes. These dyes have been known since the beginning of the 20th century, but they were not greatly exploited u n t i l the 1950s when Harmon Colors (now part of Mobay Chemical Corp.), under the d i r e c t i o n of Vincent Vesce, systematically investigated and introduced an expanded range of vat pigments to the market place (11 » 12). A number of thioindigo derivatives were sold i n i t i a l l y , but as weatherfastness requirements became more stringent, we are l e f t today with only the tetrachlorothioindigo Pigment Red 88 (XVI) (Scheme VI) as a suitable colorant with color and fastness properties similar to those of quinacridone violet (33). I n t e r e s t i n g l y , as i n the case of quinacridone, t h i s thioindigo did not make a good vat dye. However, the substituents ortho to the carboxyl and s u l f u r groups are e s s e n t i a l for i t s superior i n s o l u b i l i t y and l i g h t f a s t n e s s . Obviously, no hydrogen bonding i s possible i n the case of thioindigo, and the chlorines may s t a b i l i z e the molecule either e l e c t r o n i c a l l y or sterically. Another i n t e r e s t i n g example of such s t a b i l i z a t i o n w i l l be discussed l a t e r i n reference to isoindolinone pigments.


53.



STEP 1.

FIRST CONDENSATION

C0 H

NH

2

C0 H

R

2

STEP 2.

|°2 u H

2

l

C0 H 2

SECOND CONDENSATION

Ç02H

m

z

La» STEP 3.

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Color Pigments

H

"«

C0 H 2

"

RING CLOSURE

ix Mr" Scheme IV.

Quinacridone v i a stepwise condensation.

„

X=CH

xii

X=CI

3

P.R. 122 P.R.202



1280 APPLIED POLYMER SCIENCE


53.

STEP 1,

1281

Color Pigments


CONDENSATION

©Sic®


ACID

STEP 2,

RING CLOSURE

Scheme V. Synthesis of quinacridonequinone.

STEP 1.

SUlfONATION - REDUCTION CI

SH

1. CISO3H 2. Zr> CI STEP 2. CONDENSATION CI

^SH OT

+

c

,

c

h

2

c

o

2

h

—

—

>

CH

CQ

7

C0 H 2

CI

CI STEP 3. RING CLOSURE ÇI

CI ACID

^k^S^

ΟΓ STEP H.

[ Cl OXIDATION

f"

2

C0 H 2

r^\T \ S

>

LOI> Τ CI

Ο

2 CO CI

XVI P.R. 88

CI

Scheme VI. Synthesis of thioindigo.



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Structures XVII and XVIII show two outstanding yellow vat pigments, flavanthrone, Pigment Yellow 24 (XVII), and anthrapyrimidine, Pigment Yellow 108 (XVIII).. Unfortunately, high cost has d r a s t i c a l l y reduced t h e i r usage today. Another superior vat color i s indanthrone blue, Pigment Blue 22 (XIX) (Scheme V I I ) . In c e r t a i n uses i t i s even more weatherfast than copper phthalocyanine (34). I t i s used to redden phthalocyanines, but, again, high cost l i m i t s i t s market. There are also outstanding vat pigments i n the orange range including orange GR, Pigment Orange 43 (XX) (Scheme V I I I ) , brominated anthanthrone, Pigment Red 168 (XXII) (Scheme I X ) , and brominated pyranthrone, Pigment Red 197 (XXIIl) (Scheme X). Cost i s also a factor with the pigments, p a r t i c u l a r l y Pigment Orange 43, where the commercial methods of manufacture r e s u l t only i n a 50-55% y i e l d of the desired trans isomer. The much less desirable c i s isomer Pigment Red 194 (XXI) has a d u l l red color and bleeds badly i n solvents. Perhaps the most important class of vat pigments introduced by Harmon Colors i s the perylene family with new members being introduced frequently (35). Scheme XI outlines the general synthesis of perylene pigments, and i t i s of i n t e r e s t that even the dianhydride, Pigment Red 224, i s of commercial importance and i s sold for use i n automotive f i n i s h e s . The other perylenes f i n d broad use i n a r c h i t e c t u r a l , p l a s t i c , and i n d u s t r i a l f i n i s h e s and vary from red to v i o l e t i n hue. Isoindoline Pigments. At about the same time that quinacridone and thioindigo pigments were being developed, research on a new class of yellow pigments was being carried out by Geigy, now a part of CibaGeigy (36, 37). The f i r s t of these t e t r a c h l o r o i s o i n d o l i n i n e pigments was introduced i n the late 1950s and have been important as replacements for the increasingly more expensive flavanthrone and anthrapyrimidine yellows. Scheme XII shows the general structure of these pigments. When the diamine i s varied, yellow to dark red pigments can be prepared. Two important commercial yellows, one from jD-phenylenediamine, Pigment Yellow 110 (XXIV), and the other from 2,6-diaminotoluene, Pigment Yellow 109 (XXV), have found use i n automotive f i n i s h e s . P r i o r to the research at Geigy, the class of isoindolinones had been looked at as p o t e n t i a l colorants; however, i t was the Geigy chemists v/ho discovered that the chlorine substituents are v i t a l to produce pigments with acceptable weatherfastness and i n s o l u b i l i t y for commercial use as was shown e a r l i e r to be the case for the thioindigo, Pigment Red 88. Azo Pigments. One of the oldest and most diverse groups of pigments available i s the azo pigments. They cover the complete color gamut from yellows to reds to blues as shown i n Scheme X I I I ; b a s i c a l l y what i s required to synthesize them i s a diazotizable aromatic amine that can be coupled either at an e l e c t r o n - r i c h p o s i t i o n on an aromatic ring (XXVI), Pigment Red 1 (Para Red), or to an active methylene p o s i t i o n (XXVII), Pigment Yellow 1. I t i s clear that almost an i n f i n i t e number of substituents can be introduced either on the amine or the coupler. A vast number of such azos has been prepared over the l a s t 100 years (38). Among the



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LERNER AND SALTZMAN

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Color Pigments

P.B. 22

Scheme VII.

Synthesis of indanthrone blue.

XX P.O. 43

Scheme V I I I .

XXI

P. R. 19f|

Synthesis of orange GR.




1284

Scheme X. Synthesis of brominated pyrantharone.


53.

1285

Color Pigments

LERNER AND SALTZMAN

— CH

—

O

P.R. 179

3

E

t

P.R- 123


—/0)

P.R. 119

OCH

P.R. 190

3

P.R, 22*1

P.V. 29

Scheme XI.

Synthesis of perylene pigments.

CI

N-AR-N

CI

0

CI CI

cr CI

ο XXIV

PY 110

AR

CH

Scheme X I I .

CI

3

Tetrachloroisoindolinone synthesis.

HQ

ÇH N0

mi P. R I 3

0^CH

2

H-JC-O-N^X" +

NO,

ÇH

3

2

' Η

ο/ Λ / Ν

ή) XXVII

BY 1 Scheme X I I I .

Αζο synthesis.



1286


most successful have been reds based on deviations of βhydroxynaphthoic a c i d (BON) such as Pigment Red 22 (XXVIII), where an amide has been formed from the BON acid group and a n i l i n e . Amide formation helps to i n s o l u b i l i z e the pigment formed. Another successful group of BON-derived pigments u t i l i z e s various sulfonated derivatives of BON. The r e s u l t i n g dye i s i n s o l u b i l i z e d by forming insoluble metal s a l t s such as seen with Permanent Red 2B, Pigment Red 48 (XXIX). The banning of lead chromate pigments has resulted i n an enormous demand f o r yellow azo pigments as replacements. Pigment Yellow 74 (XXX) has become important as such a replacement i n the past 10 years. The structure i s written i n the hydrazone form. There has been evidence over recent years that t h i s i s the preferred tautomeric form of these types of pigments i n the s o l i d state (3941) versus the more commonly shown azo form (XXXI). Pigment Yellow 74 shows more color strength than other simple azos of t h i s type, presumably due to a higher e x t i n c t i o n c o e f f i c i e n t with the n i t r o group i n the para rather than the more common ortho p o s i t i o n (42) such as i n Pigment Yellow 65 (XXXII). When Pigment Yellow 74 was f i r s t introduced, i t s weather fastness was only f a i r . Improvements were made by increasing the p a r t i c l e s i z e of the pigment. The larger c r y s t a l l i t e leads to a weaker color but s t i l l with strength comparable to other azos and greatly improved weatherfastness and hiding power (43). More c a r e f u l control of c r y s t a l l i t e s i z e and d i s t r i b u t i o n has been used i n recent years for many d i f f e r e n t pigments to optimize various properties (44-47). Another d i r e c t i o n to improve the fastness properties of azos was taken by chemists at Ciba (now Ciba-Geigy). They developed a p r a c t i c a l method to form high molecular weight azos (48, 49). Decreased s o l u b i l i t y and increased melting point improve l i g h t fastness and thermal s t a b i l i t y . Scheme XIV shows the general procedure, which c a l l s f o r carrying out an aqueous coupling with a carboxylic acid containing amine followed by the f i n a l condensation step i n an organic solvent. Pigment Red 144 (XXXIII) and Pigment Yellow 93 (XXXIV) are made i n t h i s manner. They f i n d extensive use i n p l a s t i c s and f i b e r s . Another approach to improved azos i s to i n s o l u b i l i z e them v i a amide groups. Amines and acetoacetanilides based on aminobenzimidazolones have been exploited by Hoechst (50, 51). Examples are Pigment Red 171 (XXXV) and Pigment Orange 36"TxXXVI). The pigments i n t h i s series range from yellow to maroon and generally show very good heat s t a b i l i t y and good weatherfastness, especially in masstone, although, i n d i l u t i o n , they are not up to automotive standards. Other azo pigments have been produced containing various amide or sulfonamide groups such as Pigment Yellow 97 (XXXVIl) and Pigment Red 146 (XXXVIII). Miscellaneous. In t h i s section w i l l be discussed a number of i n d i v i d u a l pigments that, as of today, are represented by only one successful product, where future developments might be expected, and other areas where there has been much patent a c t i v i t y . One such pigment i s Carbazole V i o l e t , Pigment V i o l e t 23 (XXXIX) (52) synthesized as shown i n Scheme XV. I t i s a b r i l l i a n t violet


53.


CH

°2

1287

Color Pigments


H O C O N H ^

3

W

N

XXVIII RR.22

SO3

HO

CO"

Ο

a

y+2

M-Ca^Srer Mn

XXIX R R. 4 8


1288


-COCI + H N - A - N H 2

Ν

2

Ν

M

Ν

W

1

« i

1

R

R

R


Scheme XIV. Synthesis of condensation azos.

xxxv P. R, 171

XXXVI P. 0. 36




0CH

1289

Color Pigments

3

0CH

3

.C. ^CSw

0 C H

3

H-N

Ν 0CH

3

S02 I

N-H

STEP 1.

XXXVII

XXXVIII

P. Y. 97

P. R. M6

CONDENSATION

H

C H 2

STEP 2.

C l

C

CI

5

H

2 5

H

OXIDATION - RING CLOSURE

H

C2H5

Ç2H5 2

?

c,

f "

H

γ

5

C H 2

5

^ XXXIX

P.V. 23

Scheme XV. Synthesis of carbazole v i o l e t .



1290


with very high t i n c t o r i a l strength and outstanding weatherfastness at a l l d i l u t i o n s . I t i s used for reddening over phthalocyanine blue to give colors closer to ultramarine blue as compared to the greenish blues normally obtained with phthalocyanines. Although t h i s class of chromophores has been known for a number of years, Pigment V i o l e t 23 has thus f a r been the only commercially successful derivative. Another unique example i s Pigment Green 10 (XL), patented by Du Pont i n 1941 (53). I t i s a n i c k e l chelate of the azo formed by coupling £-chloroaniline to 2,4-dihydroxyquinoline (Scheme XVI ). This i s the most weatherfast azo-based pigment known and i s fast to l i g h t even i n very great d i l u t i o n v/ith white. I t s major defect i s a s l i g h t s e n s i t i v i t y to acids. Although i t has an unattractive masstone, i t s very greenish yellow undertone shows to advantage i n mixtures with aluminum and titanium dioxide. Other metal chelate pigments were patented around t h i s period but did not lead to commercial products u n t i l recently. A specific example i s Pigment Yellow 129 ( X L l ) , which was not exploited for 30 years u n t i l Ciba-Geigy developed new processes and made improved products (55, 56). In a d d i t i o n , much work i n t h i s area has been carried out by BASF (XLIl) (57) and others. X L I I I (58) and XLIV (59) are further examples from the patent l i t e r a t u r e . A related nonmetallized yellow i s Pigment Yellow 139 (XLV), which although known for some time (60-62) has only recently been offered and used commercially. I t i s a nonbleeding yellow with suitable fastness for i n d u s t r i a l f i n i s h e s . Another area of i n t e r e s t to pigment researchers both i n Germany and Japan, i s quinophthalones. XLVI (63) and XLVII (64) are tv/o patented examples. Pigment Yellow 138, marketed by BASF, i s believed to be of t h i s type, and further commercial o f f e r i n g s can be expected. * The old area of anthraquinones continues to be actively researched, and recent developments incorporate many of the substituents that have been used successfully with other pigments, such as increased molecular weight and addition of amide groups to increase bleed resistance and weatherfastness. A few older anthraquinone-based pigments were mentioned e a r l i e r . Others s t i l l a v a i l a b l e today include Pigment Yellow 123 (XLVIIl) and Pigment Red 177 (XLIX). Pigment Red 177 i s used for i t s extremely transparent masstone. I t i s of p a r t i c u l a r i n t e r e s t because i t contains free amine groups normally considered detrimental to weatherfastness. However, these amines are positioned for good hydrogen bonding with the carbonyl groups, which might help explain i t s acceptable fastness properties. Other patented samples are L (65) and LI (66), which are c l o s e l y related to Pigment Yellow 123 and Pigment Red 177, respectively. Combining azos and anthraquinones i n one molecule has also been carried out and such azoanthraquinones as L I I (67) and L I I I (68) have been patented and are just recently appearing on the market. The continued introduction of new resins and more stringent performance requirements necessitates the development both of new and improved older products by pigment manufacturers. To date, t h i s challenge has been met and w i l l continue to be met i n the years ahead as present requirements become even more stringent or as new improvements become necessary.


53.


1291

Color Pigments

STEP 1. COUPLING


STEP 2. CHELATION

XL P. G. 10 Scheme XVI.

Synthesis of Pigment Green 10.

XLII



1292


XLV

P. Y, 139


LERNER AND SALTZMAN

Color Pigments


53.


1293

1294



Literature Cited 1. Gaertner, H. J. Oil Colour Chem. Assoc. 1963, 46, 13. 2. Heinle, K. Farbe Lack 1967, 73, 735. 3. Hopmeier, A. P. In "Encyclopedia of Polymer Science and Technology"; Wiley: New York, 1969; Vol. 10, pp. 157-93. 4. Inman, E. R. In "The Royal Institute of Chemistry Lecture Series 1967"; The Royal Institute of Chemistry: London, England, 1967; No. 1. 5. Kehrer, F. Chimia 1974, 28, 173-83. 6. Lenoir, J. In "The Chemistry of Synthetic Dyes"; Venkataraman, K., Ed.; Academic: New York, 1971; Vol. 5, Chap. 6. 7. Rys, P.; Zollinger, H. "Fundamentals of the Chemistry and Application of Dyes"; Wiley-Interscience: New York, 1972. 8. Lubs, Η. Α., Ed. "The Chemistry of Synthetic Dyes and Pigments"; Reinhold: New York, 1955. 9. Patton, Temple, Ed. "Pigment Handbook"; Wiley-Interscience: New York, 1973. 10. Smith, F. M.; Stead, D. M. J. Oil Colour Chem. Assoc. 1954, 37, 117-30. 11. Vesce, V. C. Off. DIR. 1959, 28(377)(Part 2), 1-48. 12. Vesce, V. C. Off. DIR. 1959, 31(414)(Part 2), 1-143. 13. Levison, II. W. "Artists Pigments"; Colorlab: Hallandale, Fla., 1976. 14. Moser, F. H.; Thomas, A. L. "Phthalocyanine Compounds"; American Chemical Society Monograph Series No. 157, American Chemical Society: Washington, D.C., 1963. 15. Dye class number according to "Colour Index," 3rd ed., Society of Dyers and Colourists and the AATCC, 1971. 16. Liebermann, H., et al. Annalen 1935, 518, 245. 17. Anitschkoff, N. Thesis, Berlin, 1934, p. 9. 18. Struve, W. S. U.S. Patent 2,821,529, 1958, and 2,844,485, 1958; Struve, W. S.; Reidinger, A. D. U.S. Patent 2,844,484, 1958. 19. Dien, C. K. U.S. Patent 3,342,823, 1967. 20. Gerson, H.; Santimauro, J. F.; Vesce, V. C. U.S. Patent 3, 257,405, 1966. 21. North, R. U.S. Patent 3,940,399, 1976 and 4,100,162, 1978. 22. Sandoz Ltd. British Patent 924 661, 1964; Chem. Abstr. 1964, 60, 699. 23. See also Pollak, P. Prog. Org. Coat. 1977, 5, 254-53. 24. Lincke, F. Farbe Lack 1970, 76, 764-75. 25. Altiparmakian, R. H.; Bohler, H.; Kaul, B. L.; Kehrer, F. Helv. Chim. Acta 1972, 55, 85-100. 26. Zaharia, C. N.; Tarabasanu-Mihailia, C. Rev. Roum Phys. 1976, 24, 335-444. 27. Labana, S. S.; Labana, L. L. Chem. Rev. 1967, 67, 1-18. 28. Jaffe, E. E.; Matrick, H. J. Org. Chem. 1968, 33, 404. Jaffe, Ε. E.; Matrick, H. U.S. Patent 3,334,102. 29. Kim, C. K.; Maggiulli, C. A. J. Heterocycl. Chem. 1979, 16, 1651-3. 30. Ehrich, F. F. U.S. Patent 3,160,510, 1964. 31. Ehrich, F. F. U.S. Patent 3,148,075, 1964. 32. Ehrich, F. F. U.S. Patent 3,607,336, 1965. f



53. LERNER AND SALTZMAN Color Pigments

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33. Fisher, W. A. "Pigment Handbook"; Wiley-Interscience: New York, 1973; Vol. 1, pp. 673-7. 34. Rys, P.; Zollinger, H. "Fundamentals of the Chemistry and Application of Dyes"; Wiley-Interscience: New York, 1972; pp. 130, 131. 35. Fisher, W. A. "Pigment Handbook"; Wiley-Interscience: New York, 1973; Vol. 1, pp. 667-72. 36. Pugin, Α.; von der Crone, J. "New Organic Pigments", Off. Dip,. 1965, 37(488), 1071-72. 37. Pugin, A. U.S. Patent 2,973,358, 1961. 38. Review on Azos: Herbst, W.; Hunger, K. Prog. Org. Coat. 1973, 6, 211-70. 39. Pendergrass, D. Β., Jr.; Paul, I. C ; Curtin, D. Y. J. Am. Chem. Soc. 1972, 94, 8730, Brown, C. J. J. Chem. Soc. A 1967, 405. 40. Mez, H. C. Ber. Bunsengesellschaft 1968, 72, 389. 41. Griffiths, J. "Colour and Constitution of Organic Molecules"; Academic: New York, 1976; pp. 189-92. 42. Johnson, R. A. U.S. Patent 3,032,546, 1962. 43. Keay, A. M. J. Coat. Technol. 1977, 49, 31-37. 44. Hafner, O. J. Paint Technol. 1975, 147, 65-69. 45. Sappok, R. J. Oil Colour Chem. Assoc. 1978, 61, 299. 46. Chromy, L.; Kaminska, E. Prog. Org. Coat. 1978, 6, 31-48. 47. Vernardakis, T. G. Dyes Pigments 1981, 2, 175. 48. Schmid, M.; Mueller, W. U.S. Patent 2,936,306, 1960. 49. Gaertner, H. J. Oil Colour Chem. Assoc. 1963, 46, 33-39. 50. Lenoir, J. "The Chemistry of Synthetic Dyes"; Reinhold: New York, 1971; Vol. V, p. 372. 51. Schilling, K.; Dietz, E. U.S. Patent 3,109,842, 1963. 52. Lenoir, J. "The Chemistry of Synthetic Dyes"; Reinhold: New York, 1971; Vol. V, p. 421. 53. Kvalnes, D. E.; Woodward, Η. E. U.S. Patent 2 396 327, 1946. 54. Schmidt, K.; Wahl, O. U.S. Patent 2 116 913, 1938. 55. Inman, E. R.; MacPherson, I. Α.; Stirling, J. A. U.S. Patent 3,700,709, 1972. 56. McCrae, J. M.; Irvine, A. M.; MacPherson, I. A. U.S. Patent 4,143,058, 1979. 57. BASF. British Patent 1,122,938, 1968. 58. Inman, E. R.; McCrae, J. M.; Midcalf, C.; Turner, A. U.S. Patent 3,364,371, 1975. 59. Dhaliwal, P. S. U.S. Patent 3,903,118, 1975. 60. Tartter, Α.; Wessbarth, O. German Aus. 1,012,406, 1957. 61. Bock, G.; Elser, W. German Offen. 2,041,999, 1972. 62. Lotsch, W. U.S. Patent 4,166,179, 1979. 63. Imahori, S.; Kaneku, M.; Ono, H. Japanese Kakai 7,650,330, 1976. 64. Fabian, W. German Offen. 2,357,077, 1975. 65. Ehrhardt, K. German Offen. 2,340,951, 1974. 66. Gerson, H. U. S. Patent 3,718,669, 1973. 67. BASF. German Offen 1,544,372 and 1,544,374, 1965. 68. Rolf, M.; Neeff, R.; Mueller, W. German Offen. 2,644,265, 1978; 2,659,676, 1978; and 2,812,635, 1979.


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