BHT

Antioxidants (qv) have a positive effect on oils when present in the proper concentration. Sterols and tocopherols, which are natural antioxidants, may be analy2ed by gas-Hquid chromatography (glc), high performance Hquid chromatography (hplc), or thin-layer chromatography (tic). Synthetic antioxidants maybe added by processors to improve the performance or shelf life of products. These compounds include butylatedhydroxyanisole (BHA), butylated hydroxytoluene (BHT), / fZ-butyUiydroquinone (TBHQ), and propyl gallate. These materials may likewise be analy2ed by glc, hplc, or tic. Citric acid (qv), which functions as a metal chelator, may also be deterrnined by glc. 

The FCC is to food-additive chemicals what the USP—NF is to dmgs. In fact, many chemicals that are used in dmgs also are food additives (qv) and thus may have monographs in both the USP—NF and in the FCC. Examples of food-additive chemicals are ascorbic acid [50-81-7] (see Vitamins), butylated hydroxytoluene [128-37-0] (BHT) (see Antioxidants), calcium chloride [10043-52-4] (see Calcium compounds), ethyl vanillin [121-32-4] (see Vanillin), ferrous fumarate [7705-12-6] and ferrous sulfate [7720-78-7] (see Iron compounds), niacin [59-67-6] sodium chloride [7647-14-5] sodium hydroxide [1310-73-2] (see lkaliand cm ORiNE products), sodium phosphate dibasic [7558-79-4] (see Phosphoric acids and phosphates), spearmint oil [8008-79-5] (see Oils, essential), tartaric acid [133-37-9] (see Hydroxy dicarboxylic acids), tragacanth [9000-65-1] (see Gums), and vitamin A [11103-57-4]. 

BHA and BHT, which are both fat soluble, are effective ia protecting animal fat from oxidation, and are often added duting the rendering process. Propyl gallate is also effective, but it has limited fat solubiUty, and turns bluish black ia the presence of iron. It is typically used as a synergist ia combination with BHA or BHT. TBHQ is most effective against oxidation ia polyunsaturated vegetable oils (qv), and is often used ia soybean oil (19). 

A.ntioxidants. PhenoHc antioxidants, added at about 0.1—0.5 phr, are usually chosen from among butylated hydroxytoluene [128-37-0] (BHT), and Nnonylphenol [104-40-5] for Hquid stabilizer formulations and bisphenol A [80-05-7] (2,2-bis-(/)-hydroxyphenyl)propane) for the soHd systems. Low melting thioesters, dilauryl thiodipropionate [123-28-4] (DLTDP) or distearyl thiodipropionate [693-36-7] (DSTDP) are commonly added along with the phenoHcs to enhance their antioxidant performance. Usually a 3 1 ratio of thiodipropionate to phenoHc antioxidant provides the desired protection. Most mixed metal stabilizer products contain the antioxidant iagredient. 

The basic metal salts and soaps tend to be less cosdy than the alkyl tin stabilizers for example, in the United States, the market price in 1993 for calcium stearate was about 1.30— 1.60, zinc stearate was 1.70— 2.00, and barium stearate was 2.40— 2.80/kg. Not all of the coadditives are necessary in every PVC compound. Typically, commercial mixed metal stabilizers contain most of the necessary coadditives and usually an epoxy compound and a phosphite are the only additional products that may be added by the processor. The requited costabilizers, however, significantly add to the stabilization costs. Typical phosphites, used in most flexible PVC formulations, are sold for 4.00— 7.50/kg. Typical antioxidants are bisphenol A, selling at 2.00/kg Nnonylphenol at 1.25/kg and BHT at 3.50/kg, respectively. Pricing for ESO is about 2.00— 2.50/kg. Polyols, such as pentaerythritol, used with the barium—cadmium systems, sells at 2.00, whereas the derivative dipentaerythritol costs over three times as much. The P-diketones and specialized dihydropyridines, which are powerful costabilizers for calcium—zinc and barium—zinc systems, are very cosdy. These additives are 10.00 and 20.00/kg, respectively, contributing significantly to the overall stabilizer costs. Hydrotalcites are sold for about 5.00— 7.00/kg. 

MAA and EAA are stable Hquids, and are shipped in nonretumable 208-L (55-gal) polyethylene-lined dmms. For bulk shipments, insulated stainless steel tank containers and tmcks provide secure protection. 2-Acetoacetoxyethyl methacrylate is a Hquid stabili2ed with radical inhibitors such as BHT [128-37-0] and has a shelf life of approximately three months. Shipment is in 60- or 208-L polyethylene-lined dmms. Acetoacetaryhdes are nicely crystalline, stable soHds and are shipped in 208-L dmms with polyethylene liners. 

Additives. Compounds are often added to the polymer at the extmder or melt homogenizer. Common additives are antioxidants (qv), thermal stabilizers, sHp agents, antiblock agents, anduv stabilizers. Popular antioxidants are 2,6-di-/-butyl-/)-cresol (BHT), octadecyl... 

The tendency of aliphatic ethers toward oxidation requires the use of antioxidants such as hindered phenoHcs (eg, BHT), secondary aromatic amines, and phosphites. This is especially tme in polyether polyols used in making polyurethanes (PUR) because they may become discolored and the increase in acid number affects PUR production. The antioxidants also reduce oxidation during PUR production where the temperature could reach 230°C. A number of new antioxidant products and combinations have become available (115,120,124—139) (see Antioxidants). 

L. B. Barry and M. C. Richardson, "A Less Volatile Performance Equivalent to BHT for Polyether Polyol Stabilization," Polyurethane World Congress 1993, Vancouver, B.C., Canada, Oct. 10—13, 1993. 

PTMEG is a polymeric ether susceptible to both thermal and oxidative degradation. It usually contains 300—1000 ppm of an antioxidant such as 2,6-di-/ f2 -butyl-4-hydroxytoluene (BHT) to prevent oxidation under normal storage and handling conditions. Thermal decomposition in an inert atmosphere starts at 210—220°C (410—430°E) with the formation of highly flammable THE. In the presence of acidic impurities, the decomposition temperature can be significantly reduced contact with acids should therefore be avoided, and storage temperatures have to be controlled to prevent decomposition to THF (261). 

For phenols with three or more alkyl substituents, trade names, abbreviations, and associative names predominate, eg, BHT and... 

Di-/ f2 -butyl-4-methylphenol, which is commonly known as BHT (butylated hydroxy toluene), is a widely used phenoHc antioxidant in the stabilization of oils, mbber, and polyolefins (44). BHT is also one of the few phenolic antioxidants approved by the FDA as a direct food additive where it is used to retard the oxidation of naturally occurring oils in food. 

Toluenesulfonic Acid. Toluene reacts readily with fuming sulfuric acid to yield toluene—sulfonic acid. By proper control of conditions, /)i7n7-toluenesulfonic acid is obtained. The primary use is for conversion, by fusion with NaOH, to i ra-cresol. The resulting high purity i7n -cresol is then alkylated with isobutylene to produce 2 (i-dii-tert-huty -para-cmso (BHT), which is used as an antioxidant in foods, gasoline, and mbber. Mixed cresols can be obtained by alkylation of phenol and by isolation from certain petroleum and coal-tar process streams. 

Butadiene reacts readily with oxygen to form polymeric peroxides, which are not very soluble in Hquid butadiene and tend to setde at the bottom of the container because of their higher density. The peroxides are shock sensitive therefore it is imperative to exclude any source of oxygen from butadiene. Addition of antioxidants like /-butylcatechol (TBC) or butylated hydroxy toluene (BHT) removes free radicals that can cause rapid exothermic polymerizations. Butadiene shipments now routinely contain about 100 ppm TBC. Before use, the inhibitor can easily be removed (247,248). Inert gas, such as nitrogen, can also be used to blanket contained butadiene (249). 

Di-/ l -butyl-4-methylphenol /2j5 i77-2/-i72,6-Di-/ l -butyl-4-methylphenol (di-/ l -butyl-/)-cresolDi-/ l -butyl-j )-cresol or butylated hydroxytoluene (BHT)) is most commonly used as an antioxidant in plastics and mbber. Use in food is decreasing because of legislation and it is being replaced by butylated hydroxy anisole (BHA) (see Antioxidants Eood additives). 

ButylatedHydroxyAnisole (BHA). This material is an oxidation inhibitor and has been accepted for use in foods where the use of butylated hydroxytoluene (BHT) is restricted (see Food additives). It is manufactured by the alkylation of 4-hydroxyanisole [150-76-5] with isobutylene that yields a mixture of 2- and S-Z fZ-butyl isomers as products (124). 

The general industry specifications are a minimum purity of 99.9 wt %. Maximum impurities are 300 ppm water and 150 ppm of the hydroperoxide of THE. Like most ethers, it is prone to forming peroxides on storage, and therefore is usually sold containing an antioxidant such as BHT. 

Di-tert-butyl-p-cresol (2,6-di-tert-butyl-4-methylphenol, butylatedhydroxytoluene, BHT) [128-37-0] M 230.4, m 71.5 , pK 12.23. Dissolved in n-hexane at room temperature, then cooled with rapid stirring, to -60°. The ppte was separated, redissolved in hexane, and the process was repeated until the mother liquor was no longer coloured. The final product was stored under N2 at 0° [Blanchard J Am Chem Soc 82 2014 7960]. Also crystd from EtOH, MeOH, benzene, n-hexane, methylcyclohexane or pet ether (b 60-80°), and dried under vacuum. 

To obtain maximum lifetime, the oxidants must not be lost during service. A major potential source of loss is the evaporation of the antioxidant. Evaporation is often observed with BHT (butylated hydroxytoluene), a monomeric phenol, and to avoid evaporation less volatile, higher molecular weight antioxidants are used (i.e. bisphenols). 

Antioxidants. Antioxidants are rarely needed because of the highly saturated nature of the polymer chains. If protection against severe environmental ageing conditions is needed, typical antioxidants (Ethanox 702, Irganox 1010) can be added. In some cases, zinc dibutyldithiocarbamate (0.05-0.2 wt%) or butylated hydroxytoluene (BHT) can be used as stabilizers. 

For hot melt adhesives there are other considerations as well in choosing an antioxidant. Primary among these are volatility and solubility. Low molecular weight antioxidants (MW <400) should be avoided, for example BHT, as these... 

---