Fluorescence lifetime spectroscopy in multiply scattering media with dyes exhibiting multiexponential decay kinetics
ABSTRACT To investigate fluorescence lifetime spectroscopy in tissue-like scattering, measurements of phase modulation as a function of modulation frequency were made using two fluorescent dyes exhibiting single exponential decay kinetics in a 2% intralipid solution. To experimentally simulate fluorescence multiexponential decay kinetics, we varied the concentration ratios of the two dyes, 3,3-diethylthiatricarbocyanine iodide and indocynanine green (ICG), which exhibit distinctly different lifetimes of 1.33 and 0.57 ns, respectively. The experimental results were then compared with values predicted using the optical diffusion equation incorporating 1) biexponential decay, 2) average of the biexponential decay, as well as 3) stretched exponential decay kinetic models to describe kinetics owing to independent and quenched relaxation of the two dyes. Our results show that while all kinetic models could describe phase-modulation data in nonscattering solution, when incorporated into the diffusion equation, the kinetic parameters failed to likewise predict phase-modulation data in scattering solutions. We attribute the results to the insensitivity of phase-modulation measurements in nonscattering solutions and the inaccuracy of the derived kinetic parameters. Our results suggest the high sensitivity of phase-modulation measurements in scattering solutions may provide greater opportunities for fluorescence lifetime spectroscopy.
Fluorescence lifetime spectroscopy is especially advantageous for quantitative biomedical spectroscopy of analytes since the measurement of fluorescence decay kinetics (rather than the fluorescence intensity) eliminates the necessity for the knowledge of the analyte-sensing fluorophore concentration. Frequency domain techniques provide measurement of fluorescence lifetime (tau) using simple relationships of the phase-delay (theta) and amplitude-attenuation (M) of the reemitted fluorescence as a function of the modulation frequency relative to intensity modulated excitation light. However, the development of fluorescence lifetime spectroscopy for near infrared (NIR) biomedical tissue diagnostics for sensing using systematically administered dyes (Hawrysz and Sevick-Muraca, 2000; Weissleder et al., 1999) or implantable devices (Qing et al., 1997; Russell et al., 1999) requires 1) deconvolving the influence of multiple scatter upon the measured emission phase-delay and amplitude-attenuation measured in the NIR wavelength region and 2) accounting for nonsingle exponential decay kinetics.
Most fluorophores capable of analyte sensing exhibit multiexponential kinetics. For example, Ca^sup 2+^ (Lakowicz and Szmacinski, 1992) and pH (Lakowicz and Szmacinski, 1993) sensing with fluorescence lifetime spectroscopy in dilute, nonscattering solutions requires determination of multiexponential decay kinetics for accurate analyte sensing. Accurate fluorescence lifetime spectroscopy in the presence of tissue-like scattering requires a model that accounts not only for photon propagation but also for multiexponential decay kinetics as well. Indeed, the fluorescence resulting from ultraviolet excitation of the normal and athlerosclerotic arterial wall also shows multiexponential decay kinetics of its excitable constitutes (Andersson-Engels et al., 1991). Because ultraviolet light does not multiply scatter in tissues, deconvolution of the influence of scatter is not necessary. In contrast, failure to properly account for multiply scattered NIR excitation and emission light in tissue or within a scattering solution can result in erroneous identification of intrinsic decay kinetics. Upon conducting phase-modulation measurements on a solution of intralipid containing the NIR excitable fluorophore, indocyanine green (ICG), Lakowicz and Abugo (1999) did not incorporate the propagation of light, yet attribute multiexponential decay kinetics to this dye, which typically exhibits single exponential decay kinetics.
Approaches to appropriately model the multiple scattering of NIR excitation and fluorescence photons and to use diffusion models for quantitative spectroscopy have been previously demonstrated (Hutchinson et al., 1996; Cerussi et al., 1997; Mayer et al., 1999) for dyes exhibiting single exponential decay kinetics. Because most dyes exhibit multiexponential decay kinetics or exist within two or more different states, lifetime spectroscopy within tissues or other scattering media must consider kinetics beyond simple, first order decay. Indeed, the presence of scattering increases the sensitivity of frequency-domain measurements and accurate kinetic models need to be considered. However, to date, there has been no attempt to perform lifetime spectroscopy of dyes exhibiting multiexponential decays in tissue-like scattering media. Herein, we present a model-based, experimental study of fluorescence involving two dyes with distinctly different lifetimes combined together at various concentration ratios in a multiply scattering medium. By varying the concentration ratios of short- and long-lived dyes, we tested the models and identify a feasible approach for quantitative characterization of multiexponential decay kinetics in tissues as well as in implantable sensors.
Dermorubin and 5-chlorodermorubin natural anthraquinone carboxylic acids as dyes for wool
Wool is dyed for the first time with a mixture of two pure natural anthraquinone carboxylic acids, dermorubin and 5-chlorodermorubin (2:1), by means of the acid dyeing technique. The anthraquinone carboxylic acids are isolated from the fungus Dermocybe sanguinea and separated by multiplicative liquid-liquid partition using a stepwise pH gradient. The color of the dyed wool is investigated in terms of the CIELAB L*, a*, and b* parameters, and color-fastnesses to light, washing, and rubbing are tested according to iso standards. The mixture of dermorubin and 5-chlorodermorubin dyes wool orange-red with good color-fastness properties. Our procedure is equivalent to the industrial winch– technique. The results indicate that wool has a high uptake for the anthraquinone carboxylic acids. Apparently, the ionic bonds between the carboxylate ions of the dye and the protonated amino groups of the wool enhance the color-fastness properties of the dyed fabric. Dermorubin and 5-chlorodermorubin have significant potential as textile dyes, affording useful alternatives to synthetic dyes.
Naturally occurring anthraquinone pigments offer significant opportunities for dyeing textiles [6, 7]. Total synthesis of substituted anthraquinones is relatively cumbersome, frequently requiring toxic reagents, such as chromic acid or mercuric salts, and producing considerable amounts of toxic waste chemicals [1, 8, 11]. Further, in a large-scale production, purification of dyestuffs after synthesis is often difficult and expensive, and therefore optimizing the process with respect to yield and purity is necessary [11]. To avoid the disadvantages or deleterious effects of heavy synthetic processes, one should realize that nature is often the best synthesizer. In biosynthetic processes, enzymes act as catalysts, and no toxic side products or wastes are produced. Nature is rich in several types of pigments, such as anthraquinones, flavonoids, and carotenoids, and one has only to discover a suitable technique for isolating the pigments from the natural source of concern. The pure natural compounds can then be used as pigments straightforwardly or as raw materials modified further by chemical means to change their properties in the desired direction.
We were interested in the fungus Dermocybe sanguinea because we knew that it is rich in several stable anthraquinone colorants. In our previous articles, we described the dyeing of synthetic and natural textile fibers with the pure natural anthraquinone aglycones, emodin and dermocybin, using different dyeing techniques [6, 7]. Polyester and polyamide fabrics were dyed with emodin and dermocybin through high-temperature (HT) disperse dyeing, and the results were excellent. With the HT dyeing technique, uptake of emodin and dermocybin was nearly 100%. The color-fastness properties for polyester were eminently good, and for polyamide they were good. With the HT-method, no additional auxiliaries were used [6]. In the mordant dyeing experiments, wool and polyamide fabrics were dyed using KAl(SO^sub 4^)^sub 2^, K^sub 2^Cr^sub 2^O^sub 7^, CuSO^sub 4^, CoSO^sub 4^, as a mordant. These experiments showed that the pure natural hydroxyanthraquinones produced uniform dyeings with good color yields. Emodin and dermocybin yielded strong yellow, red, purple, and violet colors with a 1% owf dye solution. The color-fastness results of the mordant-dyed materials varied from good to moderate [7], but when the environmental aspects were taken into account, the disadvantages of mordant dyeing became obvious, even though minimum amounts of metal salts were used in dyebaths. The residual mordants ending up wastewater and their toxicological and carcinogenic risks were our major concern. Thus, we continued our search for more environmentally friendly dyeing techniques where no further auxiliaries would be needed.
In this paper, we describe the application of a mixture of dermorubin and 5-chlorodermorubin (2:1) as acid dyes for wool. In our previous experiments, anthraquinones were purified from the anthraquinone mixtures, fractions 1 and 2, using multiple liquid-liquid partition (mLLP) [2, 3]. Dermorubin and 5-chlorodermorubin were obtained as the main compounds from the separation of the anthraquinone carboxylic acids in fraction 2. They emerged from the tube train as a sharp main peak. As explained in our previous papers [2, 5], separating dermorubin and 5-chlorodermorubin from each other was extremely difficult because of their high aggregation tendency. However, our aim was to test the dyeing properties of anthraquinone carboxcylic acids, and because both dermorubin and 5-chlorodermorubin are carboxylic acids, their separation was not necessary. This enabled us to test the dyeing properties of a 2:1 mixture of dermorubin and 5-chlorodermorubin.
Emodin and skyrin come from fungi, which were cultivated on an appropriate culture medium [4]. Roth et al [4] used Penicilliopsis clavariaeformis Solms in their experiments, but they also mentioned some Dermocybe and Cortinarius species as potential fungi. Possibly in the future, someone will produce anthraquinone pigments suitable for dyeing textiles by cultivating fungi and extracting the pigments, which can then be modified further by chemical means. Toxic side-products from the industrial-scale syntheses could diminish when natural compounds are exploited as raw materials.
Color trails: natural dyes in historic textiles get a closer look
Chemists have developed a way to extract natural dyes from ancient textiles while preserving the unique chemical characteristics of each dye. The technique enables the researchers to then identify the plant species from which the colorants came.
Determining the source of dyes could open a new window on how ancient people used natural resources, says chemist Richard Laursen of Boston University. What’s more, since plants grow within set geographic ranges, characterizing natural dyes could help archaeologists trace the movements of tribes or determine trade relations between distant communities.
Laursen and his colleague Xian Zhang, also of Boston University, used their new chemical method to analyze yellow plant dyes called flavonoids. Many dye flavonoids have attached sugar molecules that are specific to each plant.
Traditionally, textile manufacturers have used a substance known as a mordant to bind dye compounds to fibers. “It’s a practice that’s been used for thousands of years,” says Laursen. First, the textile is soaked in a solution containing the mordant, which, in most cases, is an aluminum salt. Aluminum ions penetrate the fabric’s fibers, and then, in a second bath, dye molecules bind to the ions. The result is a colored textile that holds on to its dye.
To extract the natural dyes from historical textiles for analysis, researchers have typically relied on harsh chemicals, such as hydrochloric acid, to separate the dye from the mordant. However, this process also strips away the flavonoids’ plant-identifying sugar molecules. “You lose a lot of the information this way,” says Laursen.
As they report in the April 1 Analytical Chemistry, he and Zhang extracted yellow dyes from test fabrics using different, milder reagents: ethyl-enediaminetetraacetic acid (EDTA) and formic acid. The Boston researchers tested their method on silk fibers that they had dyed with flavonoids from different natural sources, such as pagoda-tree buds from a local arboretum and onions from a supermarket.
Laursen and Zhang soaked their dyed silk samples in hydrochloric acid, EDTA, or formic acid, extracted the flavonoids, and chemically characterized the compounds. They found that the treatment in strong acid stripped away the distinguishing sugars of the flavonoid dyes, making all of the dyes appear chemically the same. The milder reagents, however, preserved the sugar signatures of the flavonoids’ sources.
The researchers also tested their method on textile fibers from a 1,000-year-old mummy in Peru. They found a new type of yellow dye, a flavonoid sulfate, that was previously unknown to archaeologists. “You wouldn’t see it using the traditional methods,” says Laursen. It turns out, he adds, that a certain group of plants in Peru and Argentina are rich in flavonoid sulfates and that there’s a long tradition of using these plants for dyeing textiles.
Irene Good, a specialist in ancient textiles at Harvard University, says the new dye-identifying technique “is extremely important and very promising.” In addition to pegging the specific plants used to make dyes, the method could reveal how natural dyes were processed by ancient people–for example, whether they dried plants or used them fresh, she says
Inks contain ultraviolet, infrared dyes
DNP-631 Ultraviolet Invisible and DNP-IR Invisible ink cartridges contains ultraviolet (UV) or infrared (IR) dyes that are only visible to the human eye when exposed to a UV or IR light source or by using a laser scanner or camera system. The inks are designed for high-speed packaging applications that use codes to customize printing services or verify and match content for track-and-trace or anti-counterfeiting. They are also designed for use in packaging applications where high-quality output on porous media is required. The print cartridge can be easily snapped in and out and the high-capacity bulk ink delivery system insures that replacements are infrequent
Dyes for dinner?
Many fruits, vegetables and flowers make great natural dyes for foods as well as fabrics. With the holidays upon us, let’s take a look at the typical American holiday dinner and find as many items as possible to make dyes.
The main course with all the trimmings are set out for all to eat and enjoy. Turkey and dressing are not on our list of dyes, but cranberries make a beautiful pink and red dye. That might be where the red stain on the white tablecloth under Aunt Millie’s place came from.
Next, we see green onions as a garnish for the giblet gravy. Green onions produce a nice shade of green, just like the grass stains on the seat of your white shorts.
The skins of the yellow onion will make a yellowish-brown dye, like the color of a piece of manila paper used in art class. Iced tea is a light brown shade and will stain the white cloth covering the table just like the cranberries.
Those walnuts will make a darker shade of brown. We just need the shells and not the insides, though. To use walnut shells, we have to soak them in water for a week or so before the dye is brown enough to color any cloth.
Carrots are not only great to eat, but they make a rich golden-orange color, like the orange part of candy corn.
But we only need the peels. The rest we can eat raw or cooked.
Spinach and all green leafy vegetables makes strong dark-green dyes. Remember the grass stain? If you don’t like to eat spinach, you can try wearing it. It might not make your morn too happy, but it will sure make you smile to know you didn’t have to swallow your spinach.
The lemon rind on your glass of iced tea makes … you guessed it … yellow, and orange rinds make orange and yellow-orange.
My personal favorite part of the meal is next: Dessert anyone? Hot baked apple pie … I hope that someone saved the peels from the yellow apples, because they make a golden yellow dye, or greenish-yellow if they were green apples.
Sweet blueberries are the blue star of the dyes. But they are more purple-blue than true blue, like on the American flag.
Raspberries are red as well as pink, and any kind of berry you can think of can be used as a dye. When you want to know what color they will be, squish one on a white paper towel (or eat a bunch of them and look at your teeth and tongue) and see what color is left from the juice.
So now you know why your morn makes you use your napkin instead of your shirt sleeve to wipe your mouth at dinner. Chances are, if you can eat it, you can wear it too!
Jeri Deo is a free-lance writer from Corpus Christi, Texas.
Study of Dyeing Behavior of Polyester Fibers with Disperse Dyes
Abstract Sorption isotherms of disperse dyes from water with small and big molecules on various polyester fibers were obtained at 130, 115, and 105°C. Isotherms were plotted using a large range of initial dye concentration. A remarkable deviation from Nernst behavior was observed for all plotted isotherms. Langmuir fitting was tested and appeared to be in good agreement with experimental curves. Distribution of disperse dyes between polyester substrate and water and the saturation solubility of these dyes in polyester fibers was compared by considering the crystallinity and surface area of the fibers.
Key words polyester, microfiber, dyeing, disperse dyes, sorption isotherms, Langmuir fitting, Nernst fitting, aggregation, crystallinity, surface area
The dyeing of polyester fibers has been widely studied. However, the modeling of the sorption isotherms of disperse dyes on polyester fibers is still the subject of discussion. In the present study the influence of fiber characteristics and dye size on sorption isotherms of disperse dyes on polyester fibers at high temperature was investigated.
A survey of the literature showed that until the 1990s a linear distribution of Nernst type has always been used as a reference for sorption isotherms of disperse dyes on polyester fibers [1-4]. In 1995, Nakumara et al. [5] proposed a dual-mode model in which they combined a Langmuir component with the Nernst classical model for the sorption isotherms of two purified disperse dyes on polyester fibers. During the last few years, some other research has led to sorption isotherms of commercial disperse dyes on polyester fibers obeying the Langmuir law, but without a convincing explanation [6, T]. The present study was performed to try to find a theoretical foundation to explain such a result
Energy Transfer Among Dyes on Particulate Solids[dagger]
Absorption and fluorescence properties of methylene blue (MB), a well-known singlet molecular oxygen photosensitizer, and its mixtures with pheophorbide-a (Pheo) sorbed on microgranular cellulose are studied, with emphasis on radiative and nonradiative energy transfer from Pheo to MB. Although pure MB builds up dimeric species on cellulose even at 2 × 10^sup -8^ mol g^sup -1^, addition of 2.05 × 10^sup -7^ mol g^sup -1^ Pheo largely inhibits aggregation up to nearly 10^sup -6^ mol g^sup -1^ MB. At the same time, the absorption spectrum of monomeric MB in the presence of Pheo differs from the spectrum in pure cellulose. Both effects reveal a strong influence of Pheo on the medium properties. A model relying entirely on experimental data is developed, through which energy transfer efficiencies can be calculated for thin and thick layers of dye-loaded cellulose. At the largest concentration of MB assuring no dye aggregation, nonradiative energy transfer efficiencies reach a maximum value of nearly 40%. This value is quite high, taking into account the low fluorescence quantum yield of Pheo, ? = 0.21, and results from the existence of high local concentrations of the acceptor within the supporting material. These results show that large energy transfer rates can exist in a system devoid of any special molecular organization.Determination of fluorescence properties in powdered solids and turbid suspensions is complicated by the simultaneous occurrence of light scattering. The problem has attracted the attention of photochemists and spectroscopists for a long time, and different methods have been developed and applied to inorganic phosphors, colored solids, and dyes adsorbed on particulate substrates (1,2). The calculation of inner filter effects has also been addressed (3) with the help of current theories of light scattering (4,5). Some time ago we developed a model based on the Kubelka-Munk theory of diffuse reflectance to account quantitatively for radiative energy transfer and inner filter effects in systems composed of a single dye sorbed onto or chemically linked to the surface of particulate materials (6), which has been recently revised and extended to the case of a dye and its fluorescing dimers (7). The usefulness of the model relies in that multiple reabsorption and reemission can be handled in a simple way based exclusively on experimental data, as no adjustable parameters appear throughout the calculation. The validity of the approach has been successfully tested for a number of cases (6-10).
When more than one kind of dye coexists at high local concentrations, singlet excitation energy transfer can take place also by nonradiative pathways superimposed to reabsorption and reemission phenomena. The aim of the present work is to introduce nonradiative energy transfer into the theory. In this and other subsequent articles of this series we wish to demonstrate that nonradiative energy transfer rates among dyes on particulate solids can be particularly large, even without the occurrence of any special ordering at the molecular level. In this article, energy transfer between pheophorbide-a (Pheo) and methylene blue (MB), on microgranular cellulose will be handled. This is a rather complex system because, together with donor-acceptor energy transfer, donor-donor and acceptor-acceptor energy migration and backward energy transfer may take place. For donor molecules with negligible overlap between emission and absorption, that is, when the donor Stokes shift is large, model equations may be further simplified (Iriel, A. and E. San Roman, to be published). Energy migration among molecules of the same kind, for example, donors or acceptors, will not appear explicitly into the model equations. However, energy migration could have an indirect effect on the value of the energy transfer efficiencies and will be treated elsewhere (Rodríguez, H. B. and E. San Román, to be published).
From the applied point of view, the present work pursues the objective of finding development tools for the design of photosensitizers, particularly for the generation of singlet molecular oxygen, which may be easily removed from the reaction medium. The problem has been addressed by several authors by attaching dyes covalently to polymers, which may be either soluble (11) or insoluble (12) in the current solvent. Though there are examples in the literature on the supramolecular arrangement of multiple dyes on a single supporting material (13), most of the reported cases are based on single, randomly distributed dyes. Coupling of dyes undergoing efficient energy transfer allows using polychromatic light for excitation and, if order is added to the molecular structure, excitation energy can be conveyed, for example, to the particle surface. In general, a compromise has to be found between the large dye concentrations needed for substantial light absorption and excited-state deactivation due to dye aggregation at such concentrations. Dye sorption, though in general not convenient for the design of practical systems, has the advantage of easily allowing the control of dye concentrations. Finally, working with thick layers of particles introduces light scattering and inner filter effects, in principle, as complicating factors. However, our experience shows that in the limit of optically thick sample modeling is relatively simple. In addition, in this way the interplay between radiative and nonradiative energy transfer can be conveniently studied
Procion Dyes - Whole earth: cool tools - Brief Article
Grocery store dyes are hot-water dyes. The secret to spectacular tie-die (and batik) is cold water Procion Dyes. These come in scores of brilliant colors, and can be found in larger art supply stores. To start with you’ll only need the smallest size they sell, an ounce or two of dry powder, plenty for maybe a hundred shirts. Dissolve the powder in clean empty squirt bottles and you are ready to go, after you soak the designated clothes in Arm and Hammer Washing Soda (sodium carbonate, for a fixative). In our experience you’ll want to maximize the concentration of the liquid colors to keep the end result brilliant Procion Dyes, 2 oz, $4 each Plus lots of other tie-dye supplies, including blank clothes from www.dharmatrading.com, 800/542-5227
Kevin (www.kk.org) is former editor of Whole Earth Review, founding editor of Wired, and an ever-alert scout for new tools and new uses for old tools. His latest book, Asia Grace, is reviewed on page 102. Kevin’s last Catalog (Winter 2000) elicited more response than any other recent issue. We’re grateful for his willingness to stir the pot again.–MKS
Aniline Dyes Information
Aniline
Aniline, phenylamine or aminobenzene (C6H5NH2) is an organic chemical compound which is a primary aromatic amine consisting of a benzene ring and an amino group. The chemical structure of aniline is shown at the right.
Synthesis
Aniline can be produced from benzene in two steps. First, benzene is nitrated (reacted with nitric acid, a form of electrophilic substitution reaction) to give nitrobenzene. Second, the nitrobenzene is reduced to give aniline. A variety of reducing agents are effective for the reduction, including H2 (with a catalyst), hydrogen sulfide, iron, zinc, or tin.
Many derivatives of aniline can be prepared similarly.In commerce three brands of aniline are distinguished—aniline oil for blue, which is pure aniline; aniline oil for red, a mixture of equimolecular quantities of aniline and ortho- and para-toluidines; and aniline oil for safranine, which contains aniline and ortho-toluidine, and is obtained from the distillate (échappés) of the fuchsine fusion. Monomethyl and dimethyl aniline are colourless liquids prepared by heating aniline, aniline hydro-chloride and methyl alcohol in an autoclave at 220°C. They are of great importance in the colour industry. Monomethyl aniline boils at 193-195°C; dimethyl aniline at 192°C.
Properties
Aniline is oily and, although colourless, it can be slowly oxidized and resinified in air to form impurities which can give it a red-brown tint. Its boiling point is 184 °C and its melting point is -6 °C. It is a liquid at room temperature.
Like most volatile amines, it possesses a somewhat unpleasant odour of rotten fish, and also has a burning aromatic taste; it is a highly acrid poison. It ignites readily, burning with a large smoky flame.
Chemically, aniline is a weak base. Aromatic amines such as aniline are generally much weaker bases than aliphatic amines. Aniline reacts with strong acids to form salts containing the anilinium (or phenylammonium) ion (C6H5-NH3+), and reacts with acyl halides (such as acetyl chloride (ethanoyl chloride), CH3COCl) to form amides. The amides formed from aniline are sometimes called anilides, for example CH3-CO-NH-C6H5 is acetanilide, for which the modern name is N-phenyl ethanamide.
The sulphate forms beautiful white plates. Although aniline is but feebly basic, it precipitates zinc, aluminium and ferric salts, and on warming expels ammonia from its salts. Aniline combines directly with alkyl iodides to form secondary and tertiary amines; boiled with carbon disulphide it gives sulphocarbanilide (diphenyl thio-urea), CS(NHC6H5)2, which may be decomposed into phenyl mustard-oil, C6H5CNS, and triphenyl guanidine, C6H5N: C(NHC6H5)2. Sulphuric acid at 180° C gives sulphanilic acid, NH2.C6H4.SO3H. Anilides, compounds in which the amino group is substituted by an acid radical, are prepared by heating aniline with certain acids; antifebrin or acetanilide is thus obtained from acetic acid and aniline. The oxidation of aniline has been carefully investigated. In alkaline solution azobenzene results, while arsenic acid produces the violet-colouring matter violaniline. Chromic acid converts it into quinone, while chlorates, in the presence of certain metallic salts (especially of vanadium), give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene, ammonia and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives para-amino phenol and para-amino diphenylamine.
Like phenols, aniline derivatives are highly reactive in electrophilic substitution reactions. For example, sulfonation of aniline produces sulfanilic acid, which can be converted to sulfanilamide. Sulfanilamide is one of the sulfa drugs which were widely used as antibacterials in the early 20th century.
Aniline and its ring-substituted derivatives react with nitrous acid to form diazonium salts. Through these, the -NH2 group of aniline can be conveniently converted to -OH, -CN, or a halide.
Uses
Originally the great commercial value of aniline was due to the readiness with which it yields, directly or indirectly, valuable dyestuffs. The discovery of mauve in 1858 by William Perkin was the first of a series of dyestuffs which are now to be numbered by hundreds. Reference should be made to the articles dyeing, fuchsine, safranine, indulines, for more details on this subject. In addition to dyestuffs, it is a starting-product for the manufacture of many drugs such as Acetaminophen/Paracetamol (Tylenol).
Currently the largest market for aniline is preparation of 4,4′-MDI, some 85% of aniline serving this market. Other uses include rubber processing chemicals (9%), herbicides (2%), and dyes and pigments (2%). [1]
History
Aniline was first isolated from the destructive distillation of indigo in 1826 by Otto Unverdorben (Pogg. Ann., 1826, 8, p. 397), who named it crystalline. In 1834, Friedrich Runge (Pogg. Ann., 1834, 31, p. 65; 32, p. 331) isolated from coal tar a substance which produced a beautiful blue colour on treatment with chloride of lime; this he named kyanol or cyanol. In 1841, C. J. Fritzsche showed that by treating indigo with caustic potash it yielded an oil, which he named aniline, from the specific name of one of the indigo-yielding plants, Indigofera anil, anil being derived from the Sanskrit nÄ«la, dark-blue, and nÄ«lÄ, the indigo plant. About the same time N. N. Zinin found that on reducing nitrobenzene, a base was formed which he named benzidam. August Wilhelm von Hofmann investigated these variously prepared substances, and proved them to be identical (1855), and thenceforth they took their place as one body, under the name aniline or phenylamine.
Its first industrial-scale use was in the manufacture of mauveine, a purple dye discovered in 1856 by William Henry Perkin.
p-toluidine, an aniline derivative, can be used in qualitative analysis to prepare carboxylic acid derivitives.
Toxicology
Aniline is toxic by inhalation of the vapour, absorption through the skin or swallowing. It causes headache, drowsiness, cyanosis, mental confusion and in severe cases can cause convulsions. Prolonged exposure to the vapour or slight skin exposure over a period of time affects the nervous system and the blood, causing tiredness, loss of appetite, headache and dizziness.[2]
Oil mixtures containing rapeseed oil denatured with aniline have been clearly linked by epidemiological and analytic chemical studies to the toxic oil syndrome that hit Spain in the spring and summer of 1981, in which 20,000 became acutely ill, 12,000 were hospitalized, and more than 350 died in the first year of the epidemic. The precise etiology though remains unknown.
Some authorities class aniline as a carcinogen, although the IARC lists it in Group 3 (not classifiable as to its carcinogenicity to humans) due to the limited and contradictary data available.
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