2-Propylheptanol 2-PH

Commercial 2-propylheptanol is supplied as a defined branched C10 primary oxo alcohol with a terminal hydroxymethyl group and a propyl substituent at the 2-position of the heptane backbone. The CAS registry number is 10042-59-8, the molecular formula is C10H22O, and the molecular mass is 158.28 g/mol. The material is manufactured through hydroformylation of butene-derived n-pentanal, removal of branched by-product aldehydes, self-aldol condensation of n-pentanal to 2-propylheptenal, and catalytic hydrogenation. This route yields a primary alcohol with a single branched alkyl chain rather than the broad isomer mixture encountered in some C9 oxo alcohol streams. At ambient temperature 2-PH is a colourless, water-white liquid with a mild oxo-alcohol odour. Published producer data list a boiling range of 212–220 °C at 101.3 kPa, density of 0.832–0.836 g/cm³ at 20 °C, and a pour point below −50 °C. Because the hydroxyl group is terminal, esterification, acrylation, and ethoxylation proceed through primary alcohol kinetics; the propyl branch adjacent to the hydroxymethyl carbon imposes steric hindrance that can reduce reaction rate relative to linear decanol under identical catalyst loadings.

A typical certificate of analysis for a high-purity grade includes the following configuration. Water content is determined by Karl Fischer titration under ASTM E203; colour is reported against platinum-cobalt references using ASTM D1209; density is measured by oscillating U-tube under ASTM D4052. Purity by capillary gas chromatography is specified at ≥99.0 wt%. Hydroxyl number is controlled between 350 mg KOH/g and 360 mg KOH/g. The boiling range is measured under ASTM D1078 and the closed-cup flash point under ASTM D93. Carbonyl number, acid number, and sulphur content are producer-specific and are typically set because residual carbonyl compounds from the oxo synthesis can generate colour bodies during downstream esterification at elevated temperature.

Why Does the C10 Branching Pattern of 2-PH Reduce Plasticizer Volatility Relative to 2-Ethylhexanol?

In the homologous oxo alcohol series, 2-ethylhexanol has a molecular mass of 130.23 g/mol and an atmospheric boiling range of approximately 184–186 °C, whereas 2-PH has a molecular mass of 158.28 g/mol and a boiling range of 212–220 °C. The additional two methylene units in 2-PH lower plasticizer vapour pressure after esterification with phthalic anhydride. 2-Ethylhexanol yields di(2-ethylhexyl) phthalate; 2-PH yields di(2-propylheptyl) phthalate. DPHP migrates more slowly through flexible PVC and generates less fogging deposit in automotive interior testing according to DIN 75201, and lower volatile loss in heat ageing according to ISO 176. The trade-off is a longer fusion time in PVC compounding because the larger branched alkyl chain diffuses more slowly into PVC primary particles during gelation.

Compared with isononanol, which is supplied as a mixed branched C9 alcohol stream from octene hydroformylation, 2-PH is a single carbon-number molecule with a narrower isomer distribution. Compared with isodecanol, which is a highly branched C10 isomer mixture from propylene oligomerisation, 2-PH contains a seven-carbon main chain with a defined propyl branch. These differences influence ester stoichiometry, final ester viscosity, and the low-temperature response of flexible PVC compounds.

During DPHP production, 2-PH and phthalic anhydride are reacted in a molar ratio of 2.2:1 to 2.6:1 in a glass-lined batch reactor equipped with a decanter and reflux condenser. Titanium alkoxide catalyst is added at 0.05–0.15 wt% based on phthalic anhydride. The reaction is maintained at 200–230 °C while water of esterification is removed azeotropically. Excess alcohol is recovered by vacuum stripping at 1–5 kPa. The higher molecular mass and branched structure of 2-PH increase the viscosity of the finished plasticizer relative to DEHP, requiring heated transfer lines and larger clearances in gear pumps during finishing.

In flexible PVC extrusion for automotive interior skins and wire insulation, DPHP from 2-PH is incorporated at 40–60 phr depending on compound hardness and service temperature. On production-scale twin-screw extruders with screw length-to-diameter ratios between 30:1 and 38:1, the gelation plateau is reached later than with DINP at equivalent loading. Torque rheometry according to ASTM D2538 typically shows a 5–10 °C increase in fusion temperature for DPHP-based compounds. Vacuum forming of interior trim therefore requires higher stock temperatures or slower line speeds. Once fusion is complete, the compound exhibits lower mass loss in hot-air ageing at 160 °C and reduced fogging deposit mass in DIN 75201 Method B. The low-temperature flexibility of DPHP-compounded PVC is generally poorer than that achieved with DEHP or DINP, so formulators add secondary plasticizers such as adipates or sebacates when cold-flex specifications are controlled by ASTM D638-14 after conditioning at −30 °C.

In plastisol compounding, high-shear dispersion in a planetary mixer at 500–1500 rpm is used; initial Brookfield viscosity measured at 20 rpm is often lower than that of an equivalent DINP plastisol because DPHP solvates PVC more slowly at ambient temperature. The storage stability of the plastisol is therefore extended, but gelation in a forced-air tunnel oven at 190–210 °C for 45–90 s may require adjustment to achieve complete film build in floor-covering and nonwoven coating lines.

When Minimum Film Formation Temperature Depression and Partitioning Outweigh Hydrolytic Stability in Latex Coatings

2-PH itself is not a coalescing agent, but ester-alcohol derivatives and high-boiling ether derivatives are screened in low-odour architectural coatings. The key difference from propylene glycol ether coalescents is the higher calculated octanol-water partition coefficient of 2-PH-derived materials, approximately 3.8 in parent alcohol form, which favours partition into the latex polymer particle. This can lower minimum film formation temperature at lower molar addition. The reference test for such evaluations is ASTM D2354; a parallel drawdown series without coalescent is used to quantify the depression in minimum film formation temperature. In practice, 2-PH-derived coalescents are limited by the hydrolytic stability of the ester bridge in acidic or alkaline formulations; exposure to ammonia-containing emulsions can hydrolyse the ester and release free alcohol odour over shelf life. Published data for this specific configuration is limited, and formulation screening must compare viscosity stability under 50 °C accelerated storage for 14 days.

Base-catalysed ethoxylation of 2-PH is carried out in stirred stainless-steel autoclaves at ethylene oxide pressure of 0.2–0.6 MPa and reaction temperature between 140 °C and 170 °C. The resulting nonionic surfactant retains a single branched alkyl tail, which lowers the gel point and pour point relative to linear C10 alcohol ethoxylates of equal ethylene oxide number. Cloud point is measured under ISO 1065:1991 and is controlled by the number of ethylene oxide units, commonly 3–9 for detergent and hard-surface cleaning concentrates. Residual unreacted alcohol is stripped at 100–150 Pa to reduce off-odour. For acrylate monomer synthesis, 2-PH is esterified with acrylic acid at 80–110 °C in the presence of acidic ion-exchange resin or sulfuric acid, with hydroquinone monomethyl ether added at 10–50 ppm as polymerisation inhibitor. The resulting 2-propylheptyl acrylate is used as a low-volatility hydrophobic monomer in pressure-sensitive adhesive formulations; homopolymer glass transition temperature is lower than that of 2-ethylhexyl acrylate because the longer alkyl side chain increases free volume.

Esterification of 2-PH with dibasic acids such as adipic acid or sebacic acid produces diester basestocks that are evaluated for low-temperature metalworking fluids and refrigeration lubricants. The branched alkyl chain reduces pour point relative to linear C10 diesters while shifting thermal decomposition onset to slightly higher temperatures. Hydrolytic stability and oxidative stability are controlled by the dibasic acid and additive package rather than by the alcohol alone, so formulators compare 2-PH adipate against trimethylolpropane esters before selecting a base fluid for ester-based compressor lubricants.

Storage, Water Uptake, and Materials Compatibility Boundaries

2-PH should be held in closed carbon steel or stainless-steel tanks. Dry-air or nitrogen blanketing is specified by producers when ambient relative humidity exceeds 60%, because primary alcohols absorb water from humid headspace and can accumulate enough moisture to affect downstream esterification catalyst activity. The closed-cup flash point of 100–108 °C means ambient storage does not usually require explosion-proof gear, but transfer above 80 °C requires conductive hose and explosion-protected pump motors. Strong oxidising agents, strong acids, and isocyanates are incompatible. The primary alcohol reacts exothermically with isocyanates to produce carbamates, and residual 2-PH contamination in polyurethane mixing systems acts as a chain terminator that reduces hard-segment molecular weight. In esterification reactors, the alcohol feed is often nitrogen-sparged before reaction to remove dissolved oxygen and reduce colour body precursors. If the alcohol is stored in unlined carbon steel over extended periods, trace iron dissolution may occur in the presence of water; producers therefore specify stainless-steel lines and pumps for high-purity grades used in colour-sensitive plasticizer and cosmetic intermediates.