Neopentyl glycols

Polyols. Several important polyhydric alcohols or polyols are made from formaldehyde. The principal ones include pentaerythritol, made from acetaldehyde and formaldehyde trimethylolpropane, made from -butyraldehyde and formaldehyde and neopentyl glycol, made from isobutyraldehyde and formaldehyde. These polyols find use in the alkyd resin (qv) and synthetic lubricants markets. Pentaerythritol [115-77-5] is also used to produce rosin/tall oil esters and explosives (pentaerythritol tetranitrate). Trimethylolpropane [77-99-6] is also used in urethane coatings, polyurethane foams, and multiftmctional monomers. Neopentyl glycol [126-30-7] finds use in plastics produced from unsaturated polyester resins and in coatings based on saturated polyesters. 

The formaldehyde demands for pentaerythritol, trimethylolpropane, and neopentyl glycol are about 7, 2, and 1%, respectively, of production. 

Glycols such as neopentyl glycol, 2,2,4-trimethyl-l,3-pentaiiediol, 1,4-cyclohexanedimethanol, and hydroxypivalyl hydroxypivalate are used in the synthesis of polyesters (qv) and urethane foams (see Foamed plastics). Their physical properties are shown in Table 1 (1 6). 

Properties Neopentyl glycol (1) 2,2,4-Trimethyl-l,3-pent anediol (7) 1,4-Cyclohexane-dimetha nof (8) Hydroxypivalyl hydroxypivalate (9)... 

Neopentyl glycol, or 2,2-dimethyl-1,3-propanediol [126-30-7] (1) is a white crystalline soHd at room temperature, soluble ia water, alcohols, ethers, ketones, and toluene but relatively iasoluble ia alkanes (1). Two primary hydroxyl groups are provided by the 1,3-diol stmcture, making this glycol highly reactive as a chemical intermediate. The gem-A methy configuration is responsible for the exceptional hydrolytic, thermal, and uv stabiUty of neopentyl glycol derivatives. 

Chemical Properties. Neopentyl glycol can undergo typical glycol reactions such as esterification (qv), etherification, condensation, and oxidation. When basic kinetic studies of the esterification rate were carried out for neopentyl glycol, the absolute esterification rate of neopentyl glycol with / -butyric acid was approximately 20 times that of ethylene glycol with / -butyric acid (7). 

Manufacture. Commercial preparation of neopentyl glycol can be via an alkah-cataly2ed condensation of isobutyraldehyde with 2 moles of formaldehyde (crossed Canni22aro reaction) (2,8). Yields are - 70%. 

Neopentyl glycol is manufactured by Eastman Chemical Co., BASF, Perstorp, Hoechst, Mitsubishi Gas, PoHoH, and Hbls. In 1993, the bulk U.S. price was 1.61/kg. 

Toxicity. Acute toxicity data for neopentyl glycol (1) are reported in Table 2. 

Uses. Neopentyl glycol is used extensively as a chemical intermediate in the manufacture of polyester resins (see Alkyd resins), polyurethane polyols (see Urethane polymers), synthetic lubricants, polymeric plasticizers (qv), and other polymers. It imparts a combination of desirable properties to properly formulated esterification products, including low color, good weathering and chemical resistance, and improved thermal and hydrolytic stabiUty. 

The weatherabihty and hydrolytic stabiUty of unsaturated polyesters based on neopentyl glycol have made it a popular intermediate for use in formulations exposed to severe conditions, eg, in gel coats for cultured marble and marine appHcations (see Coatings, marine) (13). 

Synthetic lubricants are made with neopentyl glycol in the base-stock polyester (24). Excellent thermal stabiHty and viscosity control are imparted to special high performance aviation lubricants by the inclusion of polyester thickening agents made from neopentyl glycol (25,26) (see LUBRICATION AND lubricants). Neopentyl glycol is also used to manufacture polymeric plasticizers that exhibit the improved thermal, hydrolytic, and uv stabiHty necessary for use in some exterior appHcations (27). 

Neopentyl glycol can be used for thermal energy storage by virtue of its soHd-phase transition, which occurs at 39—41°C, a temperate range useful for solar heating and cooling (28—31). 

Derivatives. A number of derivatives of neopentyl glycol have been prepared some show promise for commercial appHcations. 

Organophosphorus Derivatives. Neopentyl glycol treated with pyridine and phosphorus trichloride in anhydrous dioxane yields the cycHc hydrogen phosphite, 5,5-dimethyl-l,3-dioxaphosphorinane 2-oxide (2) (32,33). Compounds of this type maybe useful as flameproofing plasticizers, stabilizers, synthetic lubricants, oil additives, pesticides, or intermediates for the preparation of other organophosphoms compounds (see Flame retardants Phosphorus compounds). 

Acetals andKetals. Acetals of 1,3-diols are prepared by refluxing the diol with the aldehyde in the presence of an acid catalyst, even in an aqueous medium. The corresponding ketals are more difficult to prepare in aqueous solution, but cycHc ketals of neopentyl glycol, eg, 2-butyl-2-ethyl-5,5-dimethyl-l,3-dioxane (3), can be prepared if the water of reaction is removed azeotropicaHy (34). 

Cyclopropane Derivatives. 2,2-Dimethylcyclopropanenitrile [5722-11-2] (4) has been made by preparing the di-/)-toluenesulfonate of neopentyl glycol and treating the diester with potassium cyanide (35). 

Diamine. 2,2-Dimethyl-l,3-propanediamine [7328-91-8] (5) has been prepared by amination of neopentyl glycol by treating the glycol with ammonia and hydrogen at 150—250°C at 10—31 MPa (1500—4500 psig) over a Ni catalyst. The diamine is useflil for preparation of crystalline polyureas by reaction with diisocyanates (36). 

Esters. Neopentyl glycol diesters are usually Hquids or low melting soflds. Polyesters of neopentyl glycol, and in particular unsaturated polyesters, are prepared by reaction with polybasic acids at atmospheric pressure. High molecular weight linear polyesters (qv) are prepared by the reaction of neopentyl glycol and the ester (usually the methyl ester) of a dibasic acid through transesterification (37—38). The reaction is usually performed at elevated temperatures, in vacuo, in the presence of a metallic catalyst. 

Cychc carbonates are prepared in satisfactory quaUty for anionic polymerization by catalyzed transesterification of neopentyl glycol with diaryl carbonates, followed by tempering and depolymerization. Neopentyl carbonate (5,5-dimethyl-1,3-dioxan-2-one) (6) prepared in this manner has high purity (99.5%) and can be anionically polymerized to polycarbonates with mol wt of 35,000 (39). 

Manufacture. Hydroxypivalyl hydroxypivalate may be produced by the esterification of hydroxypivaUc acid with neopentyl glycol or by the intermolecular oxidation—reduction (Tishchenko reaction) of hydroxypivaldehyde using an aluminum alkoxide catalyst (100,101). 

Polyol ester turbine oils currendy achieve greater than 10,000 hours of no-drain service in commercial jet aircraft with sump temperatures ranging to over 185°C. Polyol esters are made by reacting a polyhydric alcohol such as neopentyl glycol, trimethylol propane, or pentaerythritol with a monobasic acid. The prominent esters for automotive appfications are diesters of adipic and a2elaic acids, and polyol esters of trimethylolpropane and pentaerythritol (34). 

Cy—oxo-derived acids are the principal derivatives of the C —oxo aldehydes, and ia analogy to oxo aldehyde market appHcations, are used chiedy to make neopolyol esters, ie, those based on neopentyl glycol, trimethylolpropane, or pentaerythritol. These synlubes are employed almost entirely ia aeromotive appHcations. Heptanoic acid is also employed to make tetraethylene glycol diheptanoate, a plasticizer used with poly(vinyl butyral). 

Powder coatings are formulated from the reaction product of trimethylolpropane and IPDI, blocked with caprolactam, and polyester polyols. The saturated polyester polyols are based on aromatic acid diols, neopentyl glycol, and trimellitic anhydride for further branching. To avoid the release of caprolactam in the curing reaction, systems based on IPDI dimer diols are used. 

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