lecture 15: dyes (exam 2)

what is conjugation?

*alternating single and double bonds*; indican molecule is colorless, indigo colored due to increased conjugation-- has nearly double number of alternating single & double bonds plus oxygen; electrons are "delocalized" in a conjugated system; means the electrons are not associated with a single covalent bond; electrons move between the orbitals

where does color come from?

*color results from electrons absorbing and emitting energy*; aromatic rings and double bonds have lots of electrons

red dye: alizarin

alizarin extracted from the Madder Plant; alizarin is a *mordant dye—needs another chemical—a metal ion—*to treat the fabric first; depending on the pretreating metal ion, different color can be achieved with dye Aluminum mordant + Alizarin = Rose-Red Color Magnesium mordant + Alizarin = Violet Color Chromium mordant + Alizarin = Brownish-Violet Color Calcium mordant + Alizarin = Reddish-Purple Color Aluminum & Calcium mordant + Alizarin = Bright Red

mauveine

mauveine was the beginning of the synthetic dyes; previously, Tyrian Purple was only source of purple; mauveine was an enormously profitable discovery—made perkin a very wealthy man

what is the history of tyrian purple?

mythology credits Hercules with finding Tyrian purple—his dog was eating mollusks and was stained purple; 9,000 shellfish were needed to produce 1 gram of the dye; workers cracked the shells open with a pointed stick; extracted small gland and treat cloth with the extracted liquid; would initially turn pale yellow-green, then blue, then deep purple

indigo

named by famous Swedish botanist Linnaeus; 1200s—Marco Polo reports seeing indigo plants in Indus valley, hence the name Indigo; fresh leaves do not appear blue; to get blue color--Need to ferment under alkaline conditions, followed by oxidation; discovered when leaves were accidentally soaked in urine

dying with alizarin

Dying with natural pigments could be labor intensive & time-consuming 10 steps to successfully color with Alizarin: -Boil the fabric/yarn in potash -Boil in soap solution -Mordant with olive oil -Mordant with alum -Mordant with chalk -Treated with sheep dung -Treated with tanning material -Treated with tin salt -Rinsed overnight with river water -Dyed with madder (Alizarin)

what is the relationship between alizarin and alexander the great?

320 BC—Alexander the Great uses Alizarin; aluminum & Calcium mordant + Alizarin = Bright Red; ingenious use of madder extract; before critical battle with Persians, Alexander had his army splash themselves with madder juice and stagger onto battlefield; perrsians quickly attack, thinking they could easily defeat the wounded soldiers and are killed by Alexander's army

what are the antharaquinone derivatives?

Alizarin is a derivative of anthraquinone, which is colorless; depending on the number of hydroxyl groups attached, the color changes -anthraquinone(colorless) -naphthoquinone (colorless) -juglone (Walnuts) (Brown) -Lawsone (Henna) (Reddish-Orange)

what are the uses of malachite green?

Malachite green has 3 uses -as a dye (very popular) -As an antimicrobial active against the protozoan saprolegnia, which infects fish eggs in commercial aquaculture -however, mycobacterium tuberculosis have recently developed immunity -crystal Violet used sometimes as well -forensics application

blue pigments

blue was the most sought after color because it was hard to find—few plants were blue; Virgin Mary always painted with a blue robe—signals her significance as blue pigment was precious; Indigofera tinctoria -member of the legume family and source of the blue dye indigo

dyes and military uniforms

color of military uniform critical to keep track of sides; indigo used to dye American Revolutionary army uniforms; alizarin popular for dying uniforms; used to dye French Army uniforms—called Turkey Red; british also favored red uniforms—"Redcoats"

what is the relationship between wavelengths and dyes?

color of the dye depends on the wavelength of light that is reflected back rather than absorbed; if all light absorbed and no light reflected, fabric is black; if no light is absorbed, all reflected = white fabric; if only red wavelengths of light are absorbed= fabric appears green (complimentary color)

what are dyes

dyes are colored organic compounds that are incorporated into the fibers of textiles; molecular structure of these compounds allows the absorption of certain wavelengths of light from the visible spectrum

extracting dyes

extracting dyes from plants—man's earliest attempts at chemistry; extracting chemicals from roots, leaves, bark & berries; often first need to use a mordant—a compound that helps fix the color in a fabric; Early dyes were often problematic- Hard to obtain -Range was limited -Colors were not strong or faded quickly -Few were colorfast and would bleed with every washing

green dye

malachite green; not made from malachite, just called that because of color similarity

yellow dye

from the saffron crocus plant, Crocus sativus; similar structure to Beta-Carotene; saffron is obtained from the flowers stigma; used throughout the Middle Ages as a spice, medicine, perfume, and a dye

synthetic dyes

given the challenge of extracting dyes from natural sources, there was a push to develop synthetic dyes; *picric acid (Trinitrophenol) was one of the first used*: Wonderful yellow hue Easier to obtain than saffron Downside: EXPLOSIVE

what is the molecular basis for indigo?

indican-In the plants, exists with glucose attached, colorless; with fermentation under alkaline conditions, glucose removed to produce indoxol species; *indoxol reacts with oxygen in the air to produce Indigo (Also called Indigotin), which is blue*

what is malachite green's forensic application?

malachite green is also used as the dye on bait money; sprinkle the anhydrous powder version of malachite green on money; since money is also green, the thieves don't notice it; malachite green will stain their hands green for several days; the police catch them Green-Handed

what is the process for the synthetic production of indigo and tyrian purple?

production of Indigo & Tyrian Purple was labor-intensive; mollusk species used to make Tyrian Purple nearly extinct; 880-German chemist Johann Friedrich Wilhelm Adolf von Baeyer figures out synthesis of Indigo; takes 17 years for Badische Anilin und Soda Fabrik (BASF) to scale up reaction and make it commercially available annual production of indigo is more than 20M Kg; most used to dye blue jeans; synthetic route to make Tyrian Purple also found

background info on purple pigments

tyrian purple-Most valuable and expensive; by law, only royalty could wear purple; "Born to the purple"—means born to nobility; tyrian purple is a dibromo derivative of indigo; taken from the marine mollusk Murex; not much bromine on land; plentiful bromine in salt water

what was parkin's mauve?

william henry perkin -- english chemist accidentally discovered the first aniline dye, Mauveine, at age 18; attending Royal College of Chemistry (London); during Easter holiday of 1856, Perkin tried to synthesize quinine (antimalarial drug); synthesized mauveine instead—made a purple solution in ethanol; fabrics dipped in the solution held the color and did not bleed

orange pigment

β-Carotene—color of carrots, pumpkin & squash; *conjugated bonds--alternating single and double bonds*; β-Carotene has 11 conjugated double bonds; conjugation can be extended; wavelength of light of absorbed light is changed when oxygen, nitrogen, sulfur, bromine or chlorine added