Gum arabic

The Acacia senegal, pictured in a medicinal handbook: Franz Eugen Khler, Khler's Medizinal-Pflanzen (1887)

Acacia gum Gum arabic, also known as acacia gum, chaar gund, char goond, or meska, is a natural gum made of hardened sap taken from two species of the acacia tree; Acacia senegal and Acacia seyal. The gum is harvested commercially from wild trees throughout the Sahel from Senegal and Sudan to Somalia, although it has been historically cultivated in Arabia and West Asia. Gum arabic, a complex mixture of polysaccharides and glycoproteins, is used primarily in the food industry as a stabilizer. It is edible and has E number E414. Gum arabic is a key ingredient in traditional lithography and is used in printing, paint production, glue, cosmetics and various industrial applications, including viscosity control in inks and in textile industries, although less expensive materials compete with it for many of these roles. While acacia gum is now produced throughout the African Sahel, it is also still harvested and used in the Middle East. For example, Arab populations use the natural gum to make a chilled, sweetened, and flavored gelato-like dessert.

UsageAcacia gum's mixture of saccharides and glycoproteins gives it the properties of a glue and binder which is edible by humans. Other substances have replaced it in situations where toxicity is not an issue, as the proportions of the various chemicals in gum arabic vary widely and make it unpredictable. Still, it remains an important ingredient in soft drink syrups, "hard" gummy candies such as gumdrops, marshmallows, M&M's chocolate candies and edible glitter, a very popular, modern cake-decorating staple. For artists, it is the traditional binder used in watercolor paint, in photography for gum printing, and it is used as a binder in pyrotechnic compositions. It has been investigated for use in intestinal dialysis. Pharmaceuticals and cosmetics also use the gum as a binder, emulsifying agent and a suspending or viscosity increasing agent.[1] Gum arabic has been used in the past as a wine fining agent. It is an important ingredient in shoe polish, and can be used in making homemade incense cones. It is also used as a lickable adhesive, for example on postage stamps and cigarette papers. Printers employ it to stop oxidation of aluminium printing plates in the interval between processing of the plate and its use on a printing press.[citation needed]

Painting and art

Powdered gum arabic for artists, one part gum arabic is dissolved in four parts distilled water to make a liquid suitable for adding to pigments.

A selection of gouaches containing gum arabic Acacia gum (gum arabic) is used as a binder for watercolor painting because it dissolves easily in water. Pigment of any color is suspended within the acacia gum in varying amounts, resulting in

watercolor paint. Water acts as a vehicle or a diluent to thin the watercolor paint and helps to transfer the paint to a surface such as paper. When all moisture evaporates, the acacia gum binds the pigment to the paper surface. After the water evaporates, the acacia gum in the paint film increases luminosity and helps prevent the colors from lightening. Acacia gum allows more precise control over washes, because it prevents them from flowing or bleeding beyond the brush stroke. In addition, acacia gum slows evaporation of water, giving slightly longer working time.

PhotographyThe historical photography process of gum bichromate photography uses gum arabic mixed with ammonium or potassium dichromate and pigment to create a coloured photographic emulsion that becomes relatively insoluble in water upon exposure to ultraviolet light. In the final print, the acacia gum permanently binds the pigments onto the paper.

PrintmakingAcacia gum is also used to protect and etch an image in lithographic processes. Ink tends to fill into white space on photosensitive aluminum plates if they do not receive a layer of gum. In lithography, the gum etch is used to etch the most subtle gray tones. Phosphoric acid is added in varying concentrations to the acacia gum to etch the darker tones up to dark blacks. Multiple layers of gum are used after the etching process to build up a protective barrier that ensures the ink does not fill into the whitespace of the image being printed. It is also possible to print from black and white photocopies using a 50% acacia gum solution. This is carefully sponged onto the photocopy, and oil-based ink of any colour is rollered over the photocopy. The ink can be removed fairly easily from the white areas by carefully wiping with a damp sponge and the "paper plate" used to print using an etching press.

PyrotechnicsAcacia gum is also used as a water-soluble binder in fireworks composition.

Physical propertiesEffect on surface tension in liquidsAcacia gum reduces the surface tension of liquids, which leads to increased fizzing in carbonated beverages. This can be exploited in what is known as a Diet Coke and Mentos eruption.

Production

Acacia senegal from Paul Hermann Wilhelm Taubert's Leguminosae, in Engelmann (ed.): Natrliche Pflanzenfamilien. Vol. III, 3., 1891 A gummi arabicum tree in Indonesia

Acacia seyal from Paul Hermann Wilhelm Taubert's Leguminosae, in Engelmann (ed.): Natrliche Pflanzenfamilien. Vol. III, 3., 1891 While acacia gum has been harvested in Arabia, Egypt, and West Asia since antiquity, subSaharan acacia gum has a long history as a prized export. The gum exported came from the band of acacia trees which once covered much of the Sahel region: the southern littoral of the Sahara Desert running from the Atlantic to the Red Sea. Today, the main populations of gum-producing Acacia species are harvested in Mauritania, Senegal, Mali, Burkina Faso, Niger, Nigeria, Chad, Cameroon, Sudan, Eritrea, Somalia, Ethiopia, Kenya and Tanzania. Acacia senegal is tapped for gum by cutting holes in the bark, from which a product called kordofan or Senegal gum is exuded. Seyal gum, from Acacia seyal, the species more prevalent in East Africa, is collected from naturally occurring extrusions on the bark. Traditionally harvested by seminomadic desert pastoralists in the course of their transhumance cycle, acacia gum remains a main export of several African nations, including Mauritania, Niger, Chad, and Sudan. The hardened extrusions are collected in the middle of the rainy season (harvesting usually begins in July), and exported at the start of the dry season (November). Total world gum arabic exports are today (2008) estimated at 60,000 tonnes, having recovered from 19871989 and 20032005 crises caused by the destruction of trees by the desert locust. Sudan, Chad, and Nigeria, which in 2007 together produced 95% of world exports, have been in discussions to create a producers' cartel.

IsopreneIsoprene

IUPAC name[hide] 2-methyl-1,3-butadiene Other names[hide] terpene Identifiers 78-79-5 0A62964IBU C16521 Image 1 SMILES Properties C5H8 68.12 g/mol 0.681 g/cm 143.95 C 34.067 C

CAS number UNII KEGG Jmol-3D images

[show]Molecular formula Molar mass Density Melting point Boiling point

(verify) (what is: / ?) Except where noted otherwise, data are given for materials in their standard state (at 25 C, 100 kPa) Infobox references

Isoprene (short for isoterpene), or 2-methyl-1,3-butadiene, is a common organic compound with the formula CH2=C(CH3)CH=CH2. Under standard conditions it is a colorless liquid. However, this compound is highly volatile because of its low boiling point. Isoprene (C5H8) is the monomer of natural rubber and also a common structure motif to an immense variety of other naturally occurring compounds, collectively termed the isoprenoids. Molecular formula of isoprenoids are multiples of isoprene in the form of (C5H8)n, and this is termed the isoprene rule. The functional isoprene units in biological systems are dimethylallyl diphosphate (DMADP) and its isomer isopentenyl diphosphate (IDP). The singular terms isoprene and terpene are synonymous whereas the plurals isoprenes or terpenes refer to terpenoids (isoprenoids).

Natural occurrencesIsoprene is produced and emitted by many species of trees into the atmosphere (major producers are oaks, poplars, eucalyptus, and some legumes). The yearly production of isoprene emissions by vegetation is around 600 Tg, with half that coming from tropical broadleaf trees and the remainder coming from shrubs.[1] This is about equivalent to methane emission into the atmosphere and accounts for ~1/3 of all hydrocarbons released into the atmosphere. After release, isoprene is converted by free radicals (like the hydroxyl (OH) radical) and to a lesser extent by ozone [2] into various species, such as aldehydes, hydroperoxides, organic nitrates, and epoxides, which mix into water droplets and help create aerosols and haze. While most in the field acknowledges that isoprene emission effect aerosol formation, whether isoprene increases or decreases aerosol formation is debated. A second major effect of isoprene on the atmosphere is that in presence of nitric oxides (NOx) it contributes to the formation of tropospheric (lower atmosphere) ozone, which is one of the leading air pollutants in many countries. Isoprene itself is normally not regarded as a pollutant, as it is one of the natural products from plants. Formation of tropospheric ozone is only possible in presence of high levels of NOx, which comes almost exclusively from industrial activities. In fact, isoprene can have the opposite effect and quench ozone formation under low levels of NOx.

Isoprene production from plantsIsoprene is made through the methyl-erythritol 4-phosphate pathway (MEP pathway, also called the non-mevalonate pathway) in the chloroplasts of plants. One of the two end products of MEP pathway, dimethylallyl diphosphate (DMADP), is catalyzed by the enzyme isoprene synthase to form isoprene. Therefore, inhibitors that block the MEP pathway, such as fosmidomycin, also blocks isoprene formation. Isoprene emission increases dramatically with temperature and maximizes at around 40 C. This has led to the hypothesis that isoprene may protect plants against heat stress (thermotolerance hypothesis, see below). Emission of isoprene is also observed in some bacteria and this is thought to come from non-enzymatic degradations from DMADP. Regulation of isoprene emission Isoprene emission in plants is controlled both by the availability of substrate (DMADP) and by enzyme (isoprene synthase) activity. In particular, light, CO2 and O2 dependencies of isoprene emission are controlled by substrate availability, whereas temperature dependency of isoprene emission is regulated both by substrate level and enzyme activity. Biological roles Isoprene emission appears to be a mechanism that trees use to combat abiotic stresses.[5] In particular, isoprene has been shown to protect against moderate heat stresses (~ 40 C). It was proposed that isoprene emission was specifically used by plants to protect against large fluctations in leaf temperature. Isoprene is incorporated into and helps stabilize cell membranes in response to heat stress, conferring some tolerance to heat spikes. Isoprene may also confer some resistance to reactive

oxygen species. The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density, or PPFD), and leaf temperature. Thus, during the night, little isoprene is emitted from tree leaves, whereas daytime emissions are expected to be substantial during hot and sunny days, up to 25 g/(g dry-leafweight)/hour in many oak species.

Isoprene in other organismsIsoprene is the most abundant hydrocarbon measurable in the breath of humans. The estimated production rate of isoprene in the human body is 0.15 mol/(kgh), equivalent to approximately 17 mg/day for a person weighing 70 kg. Isoprene is also common in low concentrations in many foods.

Industrial productionIsoprene was first isolated by thermal decomposition of natural rubber.[9] It is most readily available industrially as a byproduct of the thermal cracking of naphtha or oil, as a side product in the production of ethylene. About 800,000 tonnes are produced annually. About 95% of isoprene production is used to produce cis-1,4-polyisoprenea synthetic version of natural rubber. Natural rubber is a polymer of isoprenemost often cis-1,4-polyisoprenewith a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins, and inorganic materials are found in high-quality natural rubber. Some natural rubber sources called gutta percha are composed of trans-1,4-polyisoprene, a structural isomer that has similar, but not identical, properties.[10]

Isoprene as a structural motifIsoprene is a common structural motif in biological systems. The isoprenoids (for example, the carotenes are tetraterpenes) are derived from isoprene. Also derived from isoprene are phytol, retinol (vitamin A), tocopherol (vitamin E), dolichols, and squalene. Heme A has an isoprenoid tail, and lanosterol, the sterol precursor in animals, is derived from squalene and hence from isoprene. The functional isoprene units in biological systems are dimethylallyl diphosphate (DMADP) and its isomer isopentenyl diphosphate (IDP), which are used in the biosynthesis of naturally occurring isoprenoids such as carotenoids, quinones, lanosterol derivatives (e.g. steroids) and the prenyl chains of certain compounds (e.g. phytol chain of chlorophyll).

1,3-Butadiene1,3-Butadiene

IUPAC name[hide] But-1,3-diene Other names[hide] Biethylene Erythrene Divinyl Vinylethylene Identifiers 106-99-0 7845 7557 JSD5FGP5VD 1010 C16450 CHEBI:39478 CHEMBL537970 EI9275000 Image 1 SMILES

CAS number PubChem ChemSpider UNII UN number KEGG ChEBI ChEMBL RTECS number Jmol-3D images

[show] InChI [show]Molecular formula Molar mass Appearance Density Melting point Boiling point Solubility in water Viscosity MSDS R-phrases S-phrases Properties C4H6 54.0916 Colourless gas or refrigerated liquid 0.64 g/cm3 at -6 C, liquid -108.9 C, 164.3 K, -164.0 F -4.4 C, 269 K, 24 F 735 ppm 0.25 cP at 0 C Hazards External MSDS R45 R46 R12 S45 S53

Main hazards Flash point

Flammable, irritative, carcinogen -85 C Related compounds Related alkenes Isoprene and dienes Chloroprene Related compounds Butane Supplementary data page Structure and n, r, etc. properties Thermodynamic Phase behaviour data Solid, liquid, gas Spectral data UV, IR, NMR, MS (verify) (what is: / ?) Except where noted otherwise, data are given for materials in their standard state (at 25 C, 100 kPa) Infobox references

1,3-Butadiene is a simple conjugated diene with the formula C4H6. It is an important industrial chemical used as a monomer in the production of synthetic rubber. When the word butadiene is used, most of the time it refers to 1,3-butadiene. The name butadiene can also refer to the isomer, 1,2-butadiene, which is a cumulated diene. However, this allene is difficult to prepare and has no industrial significance.

HistoryIn 1863, a French chemist isolated a previously unknown hydrocarbon from the pyrolysis of amyl alcohol.This hydrocarbon was identified as butadiene in 1886, after Henry Edward Armstrong isolated it from among the pyrolysis products of petroleum. In 1910, the Russian chemist Sergei Lebedev polymerized butadiene, and obtained a material with rubber-like properties. This polymer was, however, too soft to replace natural rubber in many roles, especially automobile tires. The butadiene industry originated in the years leading up to World War II. Many of the belligerent nations realized that in the event of war, they could be cut off from rubber plantations controlled by the British Empire, and sought to remove their dependence on natural rubber. In 1929, Eduard Tschunker and Walter Bock, working for IG Farben in Germany, made a copolymer of styrene and butadiene that could be used in automobile tires. Worldwide production quickly ensued, with butadiene being produced from grain alcohol in the Soviet Union and the United States and from coal-derived acetylene in Germany.

ProductionExtraction from C4 hydrocarbonsIn the United States, western Europe, and Japan, butadiene is produced as a byproduct of the steam cracking process used to produce ethylene and other olefins. When mixed with steam and briefly

heated to very high temperatures (often over 900 C), aliphatic hydrocarbons give up hydrogen to produce a complex mixture of unsaturated hydrocarbons, including butadiene. The quantity of butadiene produced depends on the hydrocarbons used as feed. Light feeds, such as ethane, give primarily ethylene when cracked, but heavier feeds favor the formation of heavier olefins, butadiene, and aromatic hydrocarbons. Butadiene is typically isolated from the other four-carbon hydrocarbons produced in steam cracking by extraction into a polar aprotic solvent such as acetonitrile, N-methylpyrrolidone, furfural, or dimethylformamide, from which it is then stripped by distillation.[3]

From dehydrogenation of n-ButaneButadiene can also be produced by the catalytic dehydrogenation of normal butane. The first such post-war commercial plant, producing 65,000 tons per year of butadiene, began operations in 1957 in Houston, Texas.[4] Prior to that, in the 1940s the U. S. War Department constructed several much larger plants in Borger, TX, Toledo, OH, and El Segundo, CA to produce synthetic rubber for the war effort as part of the United States Synthetic Rubber Program.[5]

From ethanolIn other parts of the world, including eastern Europe, China, and India, butadiene is also produced from ethanol. While not competitive with steam cracking for producing large volumes of butadiene, lower capital costs make production from ethanol a viable option for smaller-capacity plants. Two processes are in use. In the single-step process developed by Sergei Lebedev, ethanol is converted to butadiene, hydrogen, and water at 400450 C over any of a variety of metal oxide catalysts:[6] 2 CH3CH2OH CH2=CH-CH=CH2 + 2 H2O + H2

This process was the basis for the Soviet Union's synthetic rubber industry during and after World War II, and it remains in limited use in Russia and other parts of eastern Europe. In the other, two-step process, developed by the Russian chemist Ivan Ostromislensky, ethanol is oxidized to acetaldehyde, which reacts with additional ethanol over a tantalum-promoted porous silica catalyst at 325350 C to yield butadiene:[6] CH3CH2OH + CH3CHO CH2=CH-CH=CH2 + 2 H2O

This process was also used in the United States to produce government rubber during World War II, though it was not preferred because it is less economical than the butane or butene routes for the large volumes needed. It remains in use today in China and India.

From butenes1,3-Butadiene can also be produced by catalytic dehydrogenation of normal butenes. This method was also used by the United States Synthetic Rubber Program (USSRP) during World War II. The process was much more economical than the alcohol route but competed with aviation gasoline for available butene molecules. The USSRP constructed several plants in Baton Rouge and Lake Charles, LA; Houston, Baytown, and Port Neches, TX; and Torrance, CA.[5] In the 1960s, a Houston company known as "PetroTex" patented a process to produce butadiene from normal butenes by oxidative dehydrogenation using a proprietary catalyst. It is thought to be no longer practiced commercially.

For laboratory use1,3-Butadiene is inconvenient for laboratory use because it is a flammable gas subject to polymerization on storage. 3-Butadiene cyclic sulfone (sulfolene) is a convenient solid storable source for 1,3-butadiene for many laboratory purposes when the generation of sulfur dioxide byproduct in the reaction mixture is not objectionable.

UsesMost butadiene is polymerized to produce synthetic rubber. While polybutadiene itself is a very soft, almost liquid material, copolymers prepared from mixtures of butadiene with styrene and/or acrylonitrile, such as acrylonitrile butadiene styrene (ABS), acrylonitrile butadiene (NBR) and styrene-butadiene (SBR) are tough and elastic. SBR is the material most commonly used for the production of automobile tires. Smaller amounts of butadiene are used to make the nylon intermediate, adiponitrile, by the addition of a molecule of hydrogen cyanide to each of the double bonds in a process called hydrocyanation developed by DuPont. Other synthetic rubber materials such as chloroprene, and the solvent

sulfolane are also manufactured from butadiene. Butadiene is used in the industrial production of 4vinylcyclohexene via a Diels Alder dimerization reaction[7] and the vinylcyclohexene is a common impurity found in butadiene upon storage. Cyclooctadiene and cyclododecatriene are produced via nickel- or titanium-catalyzed dimerization and trimerization reactions, respectively. Butadiene is also useful in the synthesis of cycloalkanes and cycloalkenes, as it reacts with double and triple carbon-carbon bonds through the Diels-Alder reaction.

Environmental health and safetyAcute exposure results in irritation of the mucous membranes, Higher levels can result in neurological effects such as blurred vision, fatigue, headache and vertigo. Exposure to the skin can lead to frostbite.[8] Long-term exposure has been associated with cardiovascular disease, There is a consistent association with leukemia, and weaker association with other cancers.[8] 1,3 Butadiene is listed as a known carcinogen by the Agency for Toxic Substances Disease Registry and the US EPA.[9][10] The American Council for Governmental Industrial Hygienists (ACGIH) lists the chemical as a suspected carcinogen.[10] The Natural Resource Defense Council (NRDC) lists some disease clusters that are suspected to be associated with this chemical.[11] 1,3-Butadiene is also a suspected human teratogen.[12][13][14] Prolonged and excessive exposure can affect many areas in the human body; blood, brain, eye, heart, kidney, lung, nose and throat have all been shown to react to the presence of excessive 1,3-Butadiene.[15] Animal data suggest that women have a higher sensitivity to possible carcinogenic effects of butadiene over men when exposed to the chemical. This may be due to estrogen receptor impacts. While these data reveal important implications to the risks of human exposure to butadiene, more data are necessary to draw conclusive risk assessments. There is also a lack of human data for the effects of butadiene on reproductive and development shown to occur in mice, but animal studies have shown breathing butadiene during pregnancy can increase the number of birth defects, and humans have the same hormone systems as animals.[16] Storage of butadiene as a compressed, liquified gas carries a specific and unusual hazard. Over time, polymerization can begin, creating a crust of solidified material (popcorn polymer, named for its appearance) inside the cylinder. If the cylinder is then disturbed, the crust can contact the liquid and initiate an auto-catalytic polymerization. The heat released accelerates the reaction, possibly leading to cylinder rupture. Inhibitors are typically added to reduce this hazard, but butadiene cylinders should still be considered short-shelf life items. YUUHARA