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Isopropyl alcohol
Isopropyl alcohol
Isopropyl alcohol
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Isopropyl alcohol
Skeletal formula of isopropyl alcohol
Skeletal formula of isopropyl alcohol
Ball-and-stick model of isopropyl alcohol
Ball-and-stick model of isopropyl alcohol
Names
Preferred IUPAC name
Propan-2-ol[2]
Other names
2-Propanol
Isopropanol[1]
Rubbing alcohol
sec-Propyl alcohol
2-Hydroxypropane
i-PrOH
Dimethyl carbinol
IPA
Identifiers
3D model (JSmol)
635639
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.601 Edit this at Wikidata
1464
KEGG
RTECS number
  • NT8050000
UNII
UN number 1219
  • InChI=1S/C3H7OH/c1-3(2)4/h3-4H,1-2H3 checkY
    Key: KFZMGEQAYNKOFK-UHFFFAOYSA-N checkY
  • CC(O)C
Properties
C3H8O
Molar mass 60.096 g/mol
Appearance Colorless liquid
Odor Pungent alcoholic odor
Density 0.786 g/cm3 (20 °C)
Melting point −89 °C (−128 °F; 184 K)
Boiling point 82.6 °C (180.7 °F; 355.8 K)
Miscible with water
Solubility Miscible with benzene, chloroform, ethanol, diethyl ether, glycerol; soluble in acetone
log P −0.16[3]
Acidity (pKa) 16.5[4]
−45.794·10−6 cm3/mol
1.3776
Viscosity 2.86 cP at 15 °C
1.96 cP at 25 °C[5]
1.77 cP at 30 °C[5]
1.66 D (gas)
Pharmacology
D08AX05 (WHO)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Flammable, mildly toxic[6]
GHS labelling:
GHS07: Exclamation mark GHS02: Flammable
Danger
H225, H302, H319, H336
P210, P261, P305+P351+P338
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
3
0
Flash point Open cup: 11.7 °C (53.1 °F; 284.8 K)
Closed cup: 13 °C (55 °F)
399 °C (750 °F; 672 K)
Explosive limits 2–12.7%
980 mg/m3 (TWA), 1225 mg/m3 (STEL)
Lethal dose or concentration (LD, LC):
  • 12800 mg/kg (dermal, rabbit)[8]
  • 3600 mg/kg (oral, mouse)
  • 5000 mg/kg (oral, rat)[8]
  • 2364 mg/kg (oral, rabbit)
  • 16,000 ppm (rat, 4 h)
  • 12,800 ppm (mouse, 3 h)[8]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 400 ppm (980 mg/m3)[7]
REL (Recommended)
 TWA 400 ppm (980 mg/m3), ST 500 ppm (1225 mg/m3)[7]
IDLH (Immediate danger)
 2000 ppm[7]
Safety data sheet (SDS) [1]
Related compounds
Related alcohols
 1-Propanol, ethanol, 2-butanol
Supplementary data page
Isopropyl alcohol (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Isopropyl alcohol (IUPAC name propan-2-ol and also called isopropanol or 2-propanol) is a colorless, flammable, organic compound with a pungent odor.[9]

Isopropyl alcohol, an organic polar molecule, is miscible in water, ethanol, and chloroform, demonstrating its ability to dissolve a wide range of substances including ethyl cellulose, polyvinyl butyral, oils, alkaloids, and natural resins. Notably, it is not miscible with salt solutions and can be separated by adding sodium chloride in a process known as salting out. It forms an azeotrope with water, resulting in a boiling point of 80.37 °C and is characterized by its slightly bitter taste. Isopropyl alcohol becomes viscous at lower temperatures, freezing at −89.5 °C, and has significant ultraviolet-visible absorbance at 205 nm. Chemically, it can be oxidized to acetone or undergo various reactions to form compounds such as isopropoxides, e.g. aluminium isopropoxide. As an isopropyl group linked to a hydroxyl group (chemical formula (CH3)2CHOH) it is the simplest example of a secondary alcohol, where the alcohol carbon atom is attached to two other carbon atoms. It is a structural isomer of propan-1-ol and ethyl methyl ether, all of which share the formula C3H8O.

It was first synthesized in 1853 by Alexander William Williamson and later produced for cordite preparation. It is produced through hydration of propene or hydrogenation of acetone, with modern processes achieving anhydrous alcohol through azeotropic distillation.

Isopropyl alcohol serves in medical settings as a rubbing alcohol and hand sanitizer, and in industrial and household applications as a solvent. It is a common ingredient in products such as antiseptics, disinfectants, and detergents. More than a million tonnes are produced worldwide annually. Isopropyl alcohol poses safety risks due to its flammability and potential for peroxide formation. Its ingestion or absorption leads to toxic effects including central nervous system depression and coma.

Properties

[edit]

Isopropyl alcohol is miscible in water, ethanol, and chloroform, as it is an organic polar molecule. It dissolves ethyl cellulose, polyvinyl butyral, many oils, alkaloids, and natural resins.[10] Unlike ethanol or methanol, isopropyl alcohol is not miscible with salt solutions and can be separated from aqueous solutions by adding a salt such as sodium chloride. The process is colloquially called salting out, and causes concentrated isopropyl alcohol to separate into a distinct layer.[11]

Isopropyl alcohol forms an azeotrope with water, which gives a boiling point of 80.37 °C (176.67 °F) and a composition of 87.7% by mass (91% by volume) isopropyl alcohol. It has a slightly bitter taste, and is toxic when ingested.[11][12]

Isopropyl alcohol becomes increasingly viscous with decreasing temperature and freezes at −89.5 °C (−129.1 °F).[9] Mixtures with water have higher freezing points: 99% at −89.5 °C (−129.1 °F), 91% (the azeotrope) at −75.5 °C (−103.9 °F), and 70% at −61.7 °C (−79.1 °F).[13]

Isopropyl alcohol has a maximal absorbance at 205 nm in an ultraviolet-visible spectrum.[14][15]

Reactions

[edit]

Isopropyl alcohol can be oxidized to acetone, which is the corresponding ketone. This can be achieved using oxidizing agents such as chromic acid, or by dehydrogenation of isopropyl alcohol over a heated copper catalyst:

(CH3)2CHOH → (CH3)2CO + H2

Isopropyl alcohol is often used as both solvent and hydride source in the Meerwein-Ponndorf-Verley reduction and other transfer hydrogenation reactions. Isopropyl alcohol may be converted to 2-bromopropane using phosphorus tribromide, or dehydrated to propene by heating with sulfuric acid.

Like most alcohols, isopropyl alcohol reacts with active metals such as potassium to form alkoxides that are called isopropoxides. With titanium tetrachloride, isopropyl alcohol reacts to give titanium isopropoxide:

TiCl4 + 4 (CH3)2CHOH → Ti(OCH(CH3)2)4 + 4 HCl

This and similar reactions are often conducted in the presence of base.

The reaction with aluminium is initiated by a trace of mercury to give aluminium isopropoxide.[16]

History

[edit]

Isopropyl alcohol was first synthesized by the chemist Alexander William Williamson in 1853. He achieved this by heating a mixture of propene and sulfuric acid. Standard Oil produced isopropyl alcohol by hydrating propene. Isopropyl alcohol was oxidized to acetone for the preparation of cordite, a smokeless, low explosive propellant.[17]

Production

[edit]

In 1994, 1.5 million tonnes of isopropyl alcohol were produced in the United States, Europe, and Japan.[18] It is primarily produced by combining water and propene in a hydration reaction or by hydrogenating acetone.[18][19] There are two routes for the hydration process and both processes require that the isopropyl alcohol be separated from water and other by-products by distillation. Isopropyl alcohol and water form an azeotrope, and simple distillation gives a material that is 87.9% by mass isopropyl alcohol and 12.1% by mass water.[20] Pure (anhydrous) isopropyl alcohol is made by azeotropic distillation of the wet isopropyl alcohol using either diisopropyl ether or cyclohexane as azeotroping agents.[18]

Biological

[edit]

Small amounts of isopropyl alcohol are produced in the body in diabetic ketoacidosis.[21]

Indirect hydration

[edit]

Indirect hydration reacts propene with sulfuric acid to form a mixture of sulfate esters. This process can use low-quality propene, and is predominant in the USA. These processes give primarily isopropyl alcohol rather than 1-propanol, because adding water or sulfuric acid to propene follows Markovnikov's rule. Subsequent hydrolysis of these esters by steam produces isopropyl alcohol, by distillation. Diisopropyl ether is a significant by-product of this process; it is recycled back to the process and hydrolyzed to give the desired product.[18]

CH3CH=CH2 + H2O H2SO4→ (CH3)2CHOH

Direct hydration

[edit]
See also: Heteropoly acid

Direct hydration reacts propene and water, either in gas or liquid phase, at high pressures in the presence of solid or supported acidic catalysts. This type of process usually requires higher-purity propylene (> 90%).[18] Direct hydration is more commonly used in Europe.

Hydrogenation of acetone

[edit]

Isopropyl alcohol can be prepared via the hydrogenation of acetone, but this approach involves an extra step compared to the above methods, as acetone is itself normally prepared from propene via the cumene process.[18] IPA cost is primarily driven by raw material cost, and this way is economical when acetone is cheaper than propylene as a byproduct of phenol production (the coexistence of two ways on most markets allows them to balance the prices).

A known issue is the formation of MIBK and other self-condensation products. Raney nickel was one of the original industrial catalysts, modern catalysts are often supported bimetallic materials.

Uses

[edit]
One of the small scale uses of isopropyl alcohol is in cloud chambers. Isopropyl alcohol has ideal physical and chemical properties to form a supersaturated layer of vapor which can be condensed by particles of radiation.

In 1990, 45,000 metric tonnes of isopropyl alcohol were used in the United States, mostly as a solvent for coatings or for industrial processes. In that year, 5400 metric tonnes were used for household purposes and in personal care products. Isopropyl alcohol is popular in particular for pharmaceutical applications,[18] due to its low toxicity. Some isopropyl alcohol is used as a chemical intermediate. Isopropyl alcohol may be converted to acetone, but the cumene process is more significant.[18]

Solvent

[edit]

Isopropyl alcohol dissolves a wide range of non-polar compounds. It evaporates quickly and the typically available grades tend to not leave behind oil traces when used as a cleaning fluid unlike some other common solvents. It is also relatively non-toxic. Thus, it is used widely as a solvent and as a cleaning fluid, especially where there are oils or oil based residues which are not easily cleaned with water, conveniently evaporating and (depending on water content and other variables) posing less of a risk of corrosion or rusting than plain water. Together with ethanol, n-butanol, and methanol, it belongs to the group of alcohol solvents.

Isopropyl alcohol is commonly used for cleaning eyeglasses, electrical contacts, audio or video tape heads, DVD and other optical disc lenses, bongs,[22] and for removing thermal paste from heatsinks on CPUs[23] and other IC packages.

It is sometimes used by miniatures hobbyists to strip acrylic paints & primers from high impact polystyrene miniatures.[24][25][26]

Intermediate

[edit]

Isopropyl alcohol is esterified to give isopropyl acetate, another solvent. It reacts with carbon disulfide and sodium hydroxide to give sodium isopropylxanthate, which has use as an herbicide and an ore flotation reagent.[27] Isopropyl alcohol reacts with titanium tetrachloride and aluminium metal to give titanium and aluminium isopropoxides, respectively, the former a catalyst, and the latter a chemical reagent.[18] This compound may serve as a chemical reagent in itself, by acting as a dihydrogen donor in transfer hydrogenation.

Medical

[edit]

Rubbing alcohol, hand sanitizer, and disinfecting pads typically contain a 60–70% solution of isopropyl alcohol or ethanol in water. Water is required to open up membrane pores of bacteria, which acts as a gateway for isopropyl alcohol. A 75% v/v solution in water may be used as a hand sanitizer.[28] Isopropyl alcohol is used as a water-drying aid for the prevention of otitis externa, better known as swimmer's ear.[29]

Inhaled isopropyl alcohol can be used for treating nausea in some settings by placing a disinfecting pad under the nose.[30]

Early uses as an anesthetic

[edit]

Although isopropyl alcohol can be used for anesthesia, its many negative attributes or drawbacks prohibit this use. Isopropyl alcohol can also be used similarly to ether as a solvent[31] or as an anesthetic by inhaling the fumes or orally. Early uses included using the solvent as general anesthetic for small mammals[32] and rodents by scientists and some veterinarians. However, it was soon discontinued, as many complications arose, including respiratory irritation, internal bleeding, and visual and hearing problems. In rare cases, respiratory failure leading to death in animals was observed.

Automotive

[edit]

Isopropyl alcohol is a major ingredient in "gas dryer" fuel additives. In significant quantities, water is a problem in fuel tanks, as it separates from gasoline and can freeze in the supply lines at low temperatures. Alcohol does not remove water from gasoline, but the alcohol solubilizes water in gasoline. Once soluble, water does not pose the same risk as insoluble water, as it no longer accumulates in the supply lines and freezes but is dissolved within the fuel itself. Isopropyl alcohol is often sold in aerosol cans as a windshield or door lock deicer. Isopropyl alcohol is also used to remove brake fluid traces from hydraulic braking systems, so that the brake fluid (usually DOT 3, DOT 4, or mineral oil) does not contaminate the brake pads and cause poor braking. Mixtures of isopropyl alcohol and water are also commonly used in homemade windshield washer fluid.

Laboratory

[edit]

As a biological specimen preservative, isopropyl alcohol provides a comparatively non-toxic alternative to formaldehyde and other synthetic preservatives. Isopropyl alcohol solutions of 70–99% are used to preserve specimens.

Isopropyl alcohol is often used in DNA extraction. A lab worker adds it to a DNA solution to precipitate the DNA, which then forms a pellet after centrifugation. This is possible because DNA is insoluble in isopropyl alcohol.

Semiconductors

[edit]

Isopropyl alcohol is used as an additive in alkaline anisotropic etching of monocrystalline silicon, such as with potassium hydroxide or tetramethylammonium hydroxide. This process is used in texturing of silicon solar cells and microfabrication (e.g. in MEMS devices). Isopropyl alcohol increases the anisotropy of the etch by increasing the etch rate of [100] plane relative to higher indexed planes.[33]

Safety

[edit]

Isopropyl alcohol vapor is denser than air and is flammable, with a flammability range of between 2% and 12.7% in air. It should be kept away from heat, sparks, and open flame.[34] Distillation of isopropyl alcohol over magnesium has been reported to form peroxides, which may explode upon concentration.[35][36] Isopropyl alcohol can react with air and oxygen over time to form unstable peroxides that can explode.[37]

Toxicology

[edit]

Isopropyl alcohol, via its metabolites, is somewhat more toxic than ethanol, but considerably less toxic than ethylene glycol or methanol. Death from ingestion or absorption of even relatively large quantities is rare. Both isopropyl alcohol and its metabolite, acetone, act as central nervous system (CNS) depressants.[38] Poisoning can occur from ingestion, inhalation, or skin absorption.[39] Symptoms of isopropyl alcohol poisoning include flushing, headache, dizziness, CNS depression, nausea, vomiting, anesthesia, hypothermia, low blood pressure, shock, respiratory depression, and coma.[38] Overdoses may cause a fruity odor on the breath as a result of its metabolism to acetone.[40] Isopropyl alcohol does not cause an anion gap acidosis, but it produces an osmolal gap between the calculated and measured osmolalities of serum, as do the other alcohols.[38] The findings of acetone without acidosis leads to the sine qua non of "ketosis without acidosis."

Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver[38] and has a biological half-life in humans between 2.5 and 8.0 hours.[38] Unlike methanol or ethylene glycol poisoning, the metabolites of isopropyl alcohol are considerably less toxic, and treatment is largely supportive. Furthermore, there is no indication for the use of fomepizole, an alcohol dehydrogenase inhibitor, unless co-ingestion with methanol or ethylene glycol is suspected.[41]

In forensic pathology, people who have died as a result of diabetic ketoacidosis or alcoholic ketoacidosis, with no isopropyl alcohol ingestion, usually have detectable blood concentrations of isopropyl alcohol of 1 to 40 mg/dL, while those by fatal isopropyl alcohol ingestion usually have blood concentrations of hundreds of mg/dL.[21]

References

[edit]
[edit]
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Isopropyl alcohol

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from Grokipedia
Isopropyl alcohol, also known as 2-propanol or isopropanol, is a colorless, volatile, and with the C₃H₈O and a molecular weight of 60.10 g/mol. It is a secondary alcohol characterized by a sharp, musty resembling , a of 82.5 °C, a of -89.5 °C, and a of 0.786 g/cm³ at 20 °C. Widely recognized for its and properties, it is miscible with , , , and , making it versatile in industrial, pharmaceutical, and consumer applications. Commercially produced since 1920, isopropyl alcohol is primarily manufactured through the indirect hydration of derived from refining, where reacts with followed by . Alternative methods include hydration of using catalysts and the catalytic of acetone, with global production reaching approximately 2.3 million tonnes in 2022 and projected to grow to 2.9 million tonnes by 2030. Historically, it was first synthesized in 1853 by Alexander William Williamson, though modern synthesis relies on petrochemical feedstocks. As a key industrial chemical, isopropyl alcohol serves as a for resins, gums, inks, and coatings, and is essential in the production of acetone via dehydrogenation, as well as derivatives like . In pharmaceuticals and , it functions as an in (typically 70% concentration), hand sanitizers, lotions, and perfumes, while also acting as a effective against certain microorganisms, including cysts at 20% concentration. Additional applications include formulations, cleaning agents, and extraction processes in and . Despite its utility, isopropyl alcohol poses health and safety risks as a flammable substance with a flash point of 12 °C and an autoignition temperature of 399 °C, forming explosive vapors in air (LEL 2%, UEL 12.7%).

Nomenclature and structure

Names and synonyms

Isopropyl alcohol, also known by its IUPAC name propan-2-ol, is a simple alcohol with the molecular formula C₃H₈O and structural formula (CH₃)₂CHOH. Common names for this compound include isopropyl alcohol, isopropanol, 2-propanol, and dimethyl carbinol. Additional synonyms encompass sec-propyl alcohol and the abbreviated form iPrOH, which is frequently used in chemical literature and notation. Key chemical identifiers for propan-2-ol are the 67-63-0, Compound ID (CID) 3776, and United Nations number 1219 for hazardous material transport.

Molecular structure

Isopropyl alcohol has the molecular formula and features a central carbon atom that serves as the second carbon in a three-carbon chain. This central carbon is bonded to one hydroxyl group (-OH), two methyl groups (-CH₃), and one hydrogen atom (-H), forming four single covalent bonds. The representation is CH₃-CH(OH)-CH₃, depicting the -OH group attached to the middle carbon of the backbone. The geometry around the central carbon is tetrahedral, characteristic of sp³ hybridization in organic molecules with four sigma bonds and no lone pairs on the carbon. Bond angles at this carbon are approximately 109.5°, reflecting the idealized tetrahedral arrangement where the bonded atoms are positioned to minimize electron repulsion. The presence of the electronegative oxygen atom in the -OH group imparts polarity to the molecule, with the oxygen pulling electron density toward itself and creating a partial negative charge, while the hydrogens on the carbon framework bear partial positive charges. This polarity enables isopropyl alcohol to participate in hydrogen bonding, primarily as a donor through the -OH hydrogen and as an acceptor via the oxygen lone pairs.

Properties

Physical properties

Isopropyl alcohol is a colorless, volatile with a sharp, musty characteristic of . Its density is 0.786 g/cm³ at 20 °C. The is 82.5 °C, and the is −89.5 °C. The is 11.7 °C (open cup). Note that the flash point of aqueous solutions varies with concentration; for a 40% isopropyl alcohol solution in water (by volume), the flash point is 21 °C (70 °F), though it can vary slightly (e.g., 23 °C) depending on the testing method, such as closed-cup techniques. Isopropyl alcohol is miscible with , , , and . It forms an with containing 87.7 wt% isopropyl alcohol and having a of 80.4 °C. The UV absorption maximum occurs at 205 nm. The is 2.1 mPa·s at 20 °C, and the is 1.3776 at 20 °C.
PropertyValueConditions
0.786 g/cm³20 °C
82.5 °C760 mmHg
−89.5 °C-
11.7 °COpen cup
2.1 mPa·s20 °C
1.377620 °C, D line

Chemical properties

Isopropyl alcohol, also known as propan-2-ol, is classified as a secondary alcohol due to the hydroxyl group being attached to a carbon atom that is bonded to two other carbon atoms. The hydroxyl group imparts weak acidity to the molecule, with a pKa value of approximately 17.1 for the dissociation of the proton from the oxygen atom. Under normal conditions of temperature and pressure, isopropyl alcohol exhibits good and does not readily decompose. However, prolonged exposure to air and light can lead to the formation of unstable peroxides, which are potentially and require careful handling to avoid concentration through or . Isopropyl alcohol is highly flammable, with vapors capable of forming explosive mixtures in air; its is 399 °C. As a secondary alcohol, it displays typical reactivity patterns, including the potential for to alkenes or at the alpha carbon, though specific reaction conditions and products are influenced by catalysts and reagents. Thermodynamically, the for isopropyl alcohol is ΔH_f° = −317.0 kJ/mol. The of is 45.3 kJ/mol, reflecting the required to transition from to gas phase under standard conditions.

Production

Biological production

Biological production of isopropyl alcohol, also known as isopropanol, primarily occurs through anaerobic microbial processes that convert carbohydrates or other renewable feedstocks into the alcohol via metabolic pathways. These methods leverage capable of solventogenesis, where sugars like glucose or alternative substrates such as are metabolized under oxygen-limited conditions to yield isopropanol alongside byproducts like , , and acids. The process typically involves two stages: an acidogenic phase producing and butyrate, followed by a solventogenic phase where acetone is formed and subsequently reduced to isopropanol by secondary enzymes. Key organisms include natural solvent-producing bacteria such as Clostridium beijerinckii, which conducts isopropanol-butanol-ethanol (IBE) , and , which can be adapted for similar outputs. Engineered strains, particularly modified with heterologous pathways from Clostridium species, have been developed to enhance specificity and efficiency; these involve expressing genes encoding , CoA-transferase, acetoacetate decarboxylase, and isopropanol to direct carbon flux toward isopropanol. For instance, in C. beijerinckii, glucose fermentation proceeds anaerobically, with serving as an effective in co-substrate setups to boost solvent production. The simplified can be represented as: C6H12O6→(CH3)2CHOH+byproducts (via metabolic pathways)\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow (\text{CH}_3)_2\text{CHOH} + \text{byproducts (via metabolic pathways)} This equation highlights the conversion without detailing the full enzymatic steps. Yields in biological production remain relatively low compared to chemical synthesis, typically ranging from 0.04 to 0.22 g isopropanol per g of sugar for native Clostridium strains, translating to titers under 10 g/L in batch fermentations, which limits scalability due to product toxicity and inhibition. Engineered E. coli has achieved higher titers, up to 27 g/L in optimized aerobic fed-batch processes using glucose, though these are still primarily for research and biofuel exploration rather than commercial dominance. Since the 2010s, efforts have intensified to develop sustainable, carbon-negative routes, such as gas fermentation with syngas or CO₂/H₂ feedstocks using engineered acetogens, positioning biological methods as eco-friendly alternatives amid growing interest in biorefineries.

Indirect hydration

The indirect hydration of represents a classical two-step industrial method for synthesizing isopropyl alcohol, historically dominant before the widespread adoption of direct processes. In this approach, first undergoes absorption into concentrated to form isopropyl hydrogen (also known as isopropyl ester), followed by of the ester with to liberate the alcohol while regenerating the acid for reuse. The absorption step employs 70-80% at moderate pressure (typically 10-25 bar) and low temperature (20-30°C) in agitated absorbers or reactors to favor the formation of the monoester intermediate and minimize side reactions. The subsequent occurs at elevated temperatures (80-100°C), often with dilute acid or in a separate reactor, yielding crude isopropyl alcohol alongside dilute that requires reconcentration. The overall reaction can be represented by the following equations: (CH3CH=CH2+H2SO4→(CH3)2CHOSO3H\text{(CH}_3\text{CH=CH}_2 + \text{H}_2\text{SO}_4 \rightarrow (\text{CH}_3)_2\text{CHOSO}_3\text{H} (CH3)2CHOSO3H+H2O→(CH3)2CHOH+H2SO4\text{(CH}_3)_2\text{CHOSO}_3\text{H} + \text{H}_2\text{O} \rightarrow (\text{CH}_3)_2\text{CHOH} + \text{H}_2\text{SO}_4 This process achieves yields of 90-95% based on conversion, with high selectivity toward isopropyl alcohol but potential byproducts such as or acetone. It served as the primary commercial route for isopropyl alcohol production from the until the , when direct hydration methods gained prominence due to efficiency gains. A key advantage of indirect hydration is its ability to utilize low-purity refinery-grade propylene (around 70% purity), making it economical for integrating with petrochemical streams. However, the process suffers from significant drawbacks, including equipment corrosion from the strong acid and challenges in disposing of or reconcentrating spent dilute acid, which generates wastewater and environmental concerns.

Direct hydration

The direct hydration of represents the modern industrial method for synthesizing isopropyl alcohol through a one-step vapor-phase reaction between and . In this process, (C₃H₆) and excess are passed over an acidic heterogeneous , typically supported on silica (SiO₂), in a fixed-bed reactor. The reaction is equilibrium-limited, necessitating the use of excess (often a water-to- molar ratio of 5–10:1) to shift the equilibrium toward product formation and achieve practical conversions. The reaction proceeds as follows: CH2=CHCH3+H2O⇌(CH3)2CHOH\text{CH}_2=\text{CHCH}_3 + \text{H}_2\text{O} \rightleftharpoons (\text{CH}_3)_2\text{CHOH} Typical operating conditions include temperatures of 180–260 °C and pressures of 20–30 bar to maintain the reactants in the vapor phase and promote catalytic activity. Conversion per pass is limited to about 5–10% due to thermodynamic constraints, but overall yields exceed 97% through of unreacted , with selectivity to isopropyl alcohol typically above 95%. This method has become the dominant route for global production since the , accounting for approximately 75% of output due to its efficiency and scalability. Compared to older indirect hydration processes, direct hydration offers advantages such as a cleaner operation without the generation of sulfate waste streams from sulfuric acid use, lower corrosion, and reduced environmental impact. However, it requires high-purity propylene feedstock (>93% to minimize side products like propane accumulation) and precise control to avoid oligomerization or ether formation. The crude product mixture, containing isopropyl alcohol, water, unreacted propylene, and minor impurities like diisopropyl ether, undergoes purification primarily via distillation. Initial fractionation separates unreacted gases for recycling, followed by azeotropic distillation (often using cyclohexane as an entrainer) to break the isopropyl alcohol-water azeotrope and yield high-purity product (≥99%).

Acetone hydrogenation

Isopropyl alcohol can be produced industrially through the catalytic of acetone, serving as a secondary production route that is particularly viable when acetone is available as a byproduct from other processes, such as the oxidation step in phenol manufacturing via the . This method accounts for approximately 10-15% of global isopropyl alcohol production and is commonly integrated into cumene-based facilities to valorize excess acetone. The core reaction is the reduction of acetone by : \ce(CH3)2CO+H2−>(CH3)2CHOH\ce{(CH3)2CO + H2 -> (CH3)2CHOH} In the vapor-phase variant, acetone vapor is passed over a metal , typically or , at temperatures of 100–200 °C and pressures of 1–10 atm, achieving near-complete conversion in fixed-bed reactors. Alternative liquid-phase implementations use catalysts in multi-stage fixed-bed setups, often at around 180 °C and 0.8 MPa with a hydrogen-to-acetone molar ratio of 1.5:1. Yields typically exceed 99%, with selectivity to isopropyl alcohol surpassing 98% under optimized conditions, minimizing byproducts like or unreacted acetone. The process demonstrates high efficiency due to the exothermic nature of the reaction, which is managed through cooling and recycling streams to maintain steady operation. Key advantages of this route include its high selectivity and compatibility with byproduct acetone streams, reducing waste in integrated plants; however, the primary disadvantage is the relatively high cost of as a feedstock.

Reactions

Oxidation

Isopropyl alcohol, being a secondary alcohol, is readily oxidized to acetone under mild conditions. Common reagents for this transformation include (generated from and ) or (PCC), which selectively convert the alcohol to the corresponding without further over-oxidation. These reactions are typically performed by heating the mixture, with PCC often used in solvent at for milder control. The balanced equation for the mild oxidation is: (CH3)2CHOH+[O]→(CH3)2CO+H2O(CH_3)_2CHOH + [O] \rightarrow (CH_3)_2CO + H_2O where [O] represents the oxygen from the oxidant. Alternative conditions employ potassium permanganate (KMnO₄) in acidic medium or sodium dichromate (Na₂Cr₂O₇) with sulfuric acid (H₂SO₄), both yielding acetone efficiently upon refluxing. Catalytic air oxidation methods, utilizing metal oxides such as cupric oxide or chromium(III) oxide at elevated temperatures (around 200–500°C), also produce acetone selectively in vapor-phase processes. Under stronger oxidizing conditions, such as prolonged heating with excess hot, concentrated KMnO₄, isopropyl alcohol first forms acetone, which then undergoes C–C bond cleavage to yield acetic acid and . This over-oxidation is less common for synthetic purposes due to the ketone's relative stability but demonstrates the potential for complete mineralization with vigorous reagents. In applications, mild oxidation of isopropyl alcohol provides a straightforward route to acetone for . Industrially, these oxidation processes facilitate recycling by converting excess isopropyl alcohol back to acetone, which can subsequently be hydrogenated to regenerate the alcohol.

Esterification and etherification

Isopropyl alcohol undergoes esterification with s in the presence of an acid catalyst, following the esterification mechanism, to produce the corresponding s. This reversible reaction involves the nucleophilic attack of the alcohol on the protonated , leading to the formation of and the . A representative example is the reaction with acetic acid to form , a widely used in coatings and inks. The balanced for this process is: (\ceCH3)2\ceCHOH+\ceCH3COOH⇌(\ceCH3)2\ceCHOCOCH3+\ceH2O(\ce{CH3})_2\ce{CHOH} + \ce{CH3COOH} \rightleftharpoons (\ce{CH3})_2\ce{CHOCOCH3} + \ce{H2O} This reaction typically requires heating and a strong acid catalyst such as sulfuric acid or an ion-exchange resin to shift the equilibrium toward the ester product, often achieved by removing water via distillation./Carboxylic_Acids/Reactivity_of_Carboxylic_Acids/Fischer_Esterification) In etherification, isopropyl alcohol can participate in the Williamson synthesis, where the deprotonated alkoxide reacts with an alkyl halide under basic conditions to form an ether via an SN2 mechanism. For the formation of diisopropyl ether, the isopropoxide ion derived from isopropyl alcohol reacts with isopropyl bromide. The equation is: (\ceCH3)2\ceCHOH+(\ceCH3)2\ceCHBr+\cebase→(\ceCH3)2\ceCHOCH(CH3)2+\ceHBr(\ce{CH3})_2\ce{CHOH} + (\ce{CH3})_2\ce{CHBr} + \ce{base} \rightarrow (\ce{CH3})_2\ce{CHOCH(CH3)2} + \ce{HBr} However, since both the alkoxide and halide are secondary, competing E2 elimination reactions predominate, producing propene as a major side product and limiting ether yields. Optimal conditions, such as using a polar aprotic solvent and a strong base at lower temperatures, help minimize elimination and favor ether formation, though this method is less efficient for symmetrical secondary ethers compared to acid-catalyzed dehydration./18%3A_Ethers_and_Epoxides_Thiols_and_Sulfides/18.02%3A_Preparing_Ethers)

Dehydration and other reactions

Isopropyl alcohol undergoes dehydration in the presence of an acid catalyst, such as sulfuric acid, to yield propene and water. This elimination reaction typically occurs at temperatures between 100°C and 140°C for secondary alcohols like isopropyl alcohol, though higher temperatures up to 180°C may be employed depending on the catalyst concentration and process conditions. The reaction proceeds via an E1 mechanism, involving protonation of the hydroxyl group, loss of water to form a secondary carbocation intermediate, and subsequent deprotonation to form the alkene. The balanced equation for the dehydration is: (CH3)2CHOH→H2SO4,ΔCH3CH=CH2+H2O(CH_3)_2CHOH \xrightarrow{H_2SO_4, \Delta} CH_3CH=CH_2 + H_2O
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