Why Does Tert-Butanol CAS 75-65-0 Freeze? 

If you have seen such a scene in the warehouse: for the same batch of chemicals, some drums contain clear flowing liquid, while others show white crystals like “slush“, and it smells a bit like camphor—this is likely tert-Butanol. Its special feature is: its melting point is close to the common room temperature range, temperature slightly lower may cause crystallization, slightly higher will melt again. For many people contacting it for the first time, this “state switch” is both fresh and easy to cause misunderstanding.

Besides drum position temperature difference, trace water/impurities will lower the melting point, also may lead to inconsistent solid-liquid state at same temperature (typical melting point depression phenomenon). In addition, whether crystal nucleus appears, transportation vibration etc. will affect crystallization startup (supercooling phenomenon), therefore “look like same condition but different state” situation may also appear.

We as a supplier long-term supplying tert-Butanol related products, often receive two types of questions:
“Why does it crystallize? Is it deteriorated?”
“Compared with other butanols and isopropanol, what system is it suitable for use in?”

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Who is tert-Butanol: Alias, Structure, CAS and Position in "Butanol Family"

Common writing and aliases include:
English: tert-Butanol, tert-Butyl alcohol
Abbreviation: t-BuOH, TBA (this article specifically refers to tert-butyl alcohol)
System naming: 2-methyl-2-propanol
CAS: 75-65-0

It belongs to a member of “butanol“, molecular formula is same as C4H10O. But butanol is not a single substance, but a group of isomers: molecular formula same, carbon skeleton connection method different, leading to obvious difference in physical properties and reaction performance. The four “butanol isomers” often compared together are:
n-butanol; sec-butanol; isobutanol; tert-butanol

The structure of tert-Butanol can be remembered by a very intuitive picture:
One central carbon connects three methyl groups (CH3), then connects one hydroxyl group (-OH).
This structure makes the central position very “crowded“, also commonly called steric hindrance is obvious. This is very critical for understanding later “solvent behavior” and “reaction route“.

Tert-Butanol CAS 75-65-0
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Start from "Crystallization" in Warehouse: Why tert-Butanol Solid-Liquid Switch Near Room Temperature

One of the most famous features of tert-Butanol is its melting point close to common room temperature range. Typical data given by many common materials are:
Melting point about 25°C (also common 23–26°C range expression)
Boiling point about 83°C (common 82–83°C expression)
This means: when environmental temperature fluctuates around 20 plus degrees, tert-Butanol may appear state where part is solidified and part is still liquid. Especially during transportation, warehouse night temperature drop, winter loading/unloading or air-conditioned room, this phenomenon is more common.
This is usually not deterioration, more like a “physical property reminder“: it is sensitive to temperature change.

Tert-Butanol Property Quick Check: Those Items Engineers Care About Most

When you are doing solvent selection, process scale-up or supply chain evaluation, most frequently asked is: Is it solid or liquid, is evaporation fast, can it mix with water, is it flammable, is vapor heavy. Below organize this information using “Engineering Language” (values take common public material typical values, specific batch should still refer to product data sheet and inspection report):

1. Key Properties (Typical Value Range)
Appearance: Colorless solid or colorless liquid (depends on temperature), often described having camphor-like odor
Melting point: Approx 25°C (common expression 23–26°C)
Boiling point: Approx 83°C
Density (Liquid, 25°C): Approx 0.775 g/mL (varies slightly with temperature)
Solubility in water: Compatibility with water very strong, materials often write “very good / miscible”
20°C Vapor Pressure: Materials give approx 4.1 kPa (also see similar data expressed in mmHg)
Flash Point: Approx 11–15°C (Closed cup; different materials/test methods have slight difference)
Auto-ignition Temperature: Materials often give approx 470°C
Flammable Vapor in Air Volume Fraction Range: LEL in different materials approx 1.7–2.4%, UEL common approx 8.0%, refer to SDS/local regulation standard.

Above information has two very direct conclusions:
It is easier to volatile than many “high boiling point solvents” (boiling point only 80+ degrees, vapor pressure not low);
It is more sensitive to fire source and static electricity (flash point relatively low, must manage by flammable solvent idea).

2. A Point Easily Neglected: Vapor Heavier Than Air

tert-Butanol vapor relative density greater than 1, means vapor may accumulate in poor ventilation/low places; and vapor forms explosive mixture with air easily, should manage by flammable vapor risk overall.
This is not to create tension, but to remind: in ventilation design and leakage handling, cannot only stare at “exhaust overhead”, also need to pay attention to gas accumulation risk in low space and corner area.

As Solvent: Where tert-Butanol is Useful in Formula and Process

Many customers purchasing tert-Butanol first reason is not “it is very famous”, but a more specific question:
My system has both water phase demand and organic phase dissolution demand; or I hope to adjust solubility, phase behavior, crystal form and reaction selectivity by changing solvent structure.
tert-Butanol‘s “usefulness”, often comes from three combination features:

Public materials generally describe tert-Butanol compatibility with water is strong, many commodity specifications also directly write “miscible with water“.
Value this brings to formula and process is:
You can use it to “adjust system polarity” to certain extent, instead of making choice between water and pure organic solvent;
In liquid-liquid system, it sometimes can affect phase interface behavior, thereby changing extraction efficiency or phase separation speed;
In crystallization and recrystallization process, it may also participate in system design as “solubility regulator“.
Here we deliberately do not use “universal co-solvent” saying, because in real project, solvent function always decides together with solute, temperature, impurity, agitation, concentration distribution. tert-Butanol looks more like a formula space expansion tool.

tert-Butanol as alcohol solvent, can provide typical hydrogen bond interaction. This point will play role when dissolving certain polar substances, affecting crystal form and particle morphology. It is not like some strong non-polar solvents “only responsible for dilution”, but will participate more deeply in intermolecular interaction.

tert-Butanol structure is crowded, this makes it present performance different from small molecule alcohols in certain systems. Intuitively speaking:
Same is “alcohol”, its influence on some intermolecular approach way is different;
In certain reactions and formulas, it may bring more obvious selectivity difference.
This is also why in R&D stage, many teams will take it as “structure different but still easy to obtain” solvent candidate, used to explore better system window.

As Part of Reaction System: tert-Butanol's "Chemical Character" and Common Routes

When talking about “Chemical Character“, we try to stand on process and selection angle, not writing article into classroom notes.

tert-Butanol‘s hydroxyl connects on a tertiary carbon. Engineering intuitive significance is:
Certain reactions needing “close to central carbon” will be more sensitive;
Sometimes easier to appear “form intermediate first then transform” path;
Condition design usually needs to balance system polarity, acid-base environment and temperature curve more.
You do not need to memorize reaction mechanism arrows, but suggest remembering one sentence:
tert-Butanol central site more crowded, so reaction is not “go however it wants”, needs to give it suitable channel.

Under some process conditions, tert-Butanol can dehydrate to generate isobutylene etc. flammable products. Public safety materials also will remind its possibility to decompose and generate flammable gas under strong acid condition. This dehydration/decomposition usually needs strong acid (or acidic catalyst) and certain temperature etc. conditions; under routine neutral storage and general solvent use conditions, main risk is still volatility and flammability management.
Significance of this matter on industrial chain is:
tert-Butanol can serve as “node raw material” for larger chemical tree;
When customer uses it as intermediate, supply stability, purity control and water content control importance will rise obviously.
Our common practice in project communication is: Customer first clarify “Am I treating it as solvent, or treating it as convertible raw material”, then decide priority control indicators. Two types of uses often have different sensitive points to impurities and water.

Typical Use Map: Which Scenes Choose tert-Butanol More Often

In fine chemical synthesis, process development and scale-up process, tert-Butanol common in:
As reaction solvent participating in synthesis steps;
In extraction or washing, as component adjusting polarity and compatibility;
In recrystallization and refining, used to adjust solubility curve and crystallization behavior.
If you are doing process route evaluation, situations where tert-Butanol specifically fits into candidate list usually include:
Need an organic solvent “easier to synergize with water”;
Need to utilize alcohol hydrogen bond ability, but hope solvent structure is larger, more crowded;
Hope to observe selectivity or crystallization difference through solvent structure change, and do not want to introduce solvent too strange or supply unstable.

In material and formula system, tert-Butanol often treated as:
Dissolution and dilution medium
Part of dispersion and wetting system
Cleaning solvent (especially in cleaning flow needing cooperation with water phase)
Here need to emphasize a reality point: tert-Butanol is not “replace who immediately”. It is more suitable practice to add into test matrix as “formula variable“: use 2–3 different ratios to explore compatibility, viscosity change, drying performance, residue risk etc., then decide whether to scale up.

In fuel or additive related systems, tert-Butanol is often discussed as formula component or participating in more complex product route as upstream node. (Below is common observation based on client projects, specific subject to industry and project)
For supply chain, this type of use in some projects may mean:
Demand has phasic fluctuation;
More sensitive to stable supply, batch consistency and logistics temperature control;
Customer values long-term quality trend more, not just single batch data.

tert-Butanol vs Common Alcohol Solvents: Compare by "Engineering Problem" Not "Chemical Noun"

Quality and Specification: How Suppliers Usually Define "Better to Use tert-Butanol"

“Whether tert-Butanol can be used” is easy to satisfy, but “whether can use stably, use long-term”, needs finer indicators and delivery methods.

1. Common Supply Grade (Understand by Use Scene)

Different enterprises call grade names differently, but from use angle roughly can be divided into:
Industrial Grade: Facing general synthesis, process solvent, cleaning and formula application
High Purity Grade: Facing process, analysis and R&D system sensitive to impurities
Customized Grade: Projects having clear boundaries on water content, specific impurities, color, residue, packaging cleanliness etc.
We suggest customers clarify use in inquiry stage, because biggest difference between “Industrial Grade” and “High Purity Grade” is often not in main content, but in water, volatile organic impurity profile, non-volatile residue, odor background, and inter-batch consistency.

2. Common Quality Indicators (For Contract, Acceptance and Trend Management)

In actual orders, most commonly written into indicator table usually include:
Main content (Commonly use Gas Chromatography etc. methods)
Water content (Commonly use moisture titration method)
Acidity or titratable impurity (Related to process stability)
Color and Appearance
Non-volatile residue (Very important for precision application)
Density, Refractive Index (As rapid incoming material re-check means)
Special reminder: tert-Butanol crystallization matter may affect sampling representativeness. When solid-liquid coexist, if taking liquid sample directly from upper layer, result may deviate from whole drum average value. Safer practice is:
Rewarm to uniform liquid state then mix fully then sample;
Or execute consistent action according to sampling process agreed by both sides.

3. Packaging and Delivery: Difference of Drum, IBC and Bulk Solution

tert-Butanol common packaging covers from small package to bulk delivery. For customers, packaging method is not just logistics problem, also affects:
Site drum opening frequency (More frequent more test on management)
Water introduction opportunity (More openings higher risk)
Temperature control cost (Large tank more suitable for stable temperature control, small drum easier affected by environmental temperature)
If your usage volume is relatively large, suggest including “temperature control ability, agitation circulation, filtration and metering method” into solution discussion from beginning, because stable use of tert-Butanol relies on these detail systems.

Storage and Use: Turn "Crystallization" from Trouble to Controllable Variable

Safety and Compatibility: Put Focus on "Executable Operation Habits"

tert-Butanol belongs to flammable solvent, and vapor may cause irritation to eyes and respiratory tract, high concentration environment may make people uncomfortable.
Writing safety strictly is not difficult, difficult is writing to be executable. We recommend below “landable” practices:

1. Several Hard Rules of Site Management
Maintain good ventilation, avoid vapor accumulation in local space;
Keep away from fire source, heat source and sparks, avoid heating in uncontrolled environment;
Do well in static control and grounding (Especially actions prone to generate static electricity like filling, pouring, filtration, circulation);
Use suitable personal protective equipment, avoid repeated skin contact leading to dryness or discomfort (Repeated contact may cause skin problem is common reminder);
Establish internal operation file based on Safety Data Sheet (SDS), and write “Temperature Control and Crystallization” into operation points.

2. Material Compatibility: Don’t Ignore Seals and Hoses

Public materials often remind tert-Butanol may be unfriendly to certain rubbers, plastics, existing risk of swelling or property change.
Therefore before scale-up use, suggest completing at least:
Immersion evaluation with key sealing materials (dimension change, hardness change, leakage risk);
Compatibility confirmation with hose, pump diaphragm, gasket;
If for high cleanliness application, confirm material precipitation and background residue.

FAQ: 10 Questions Most Commonly Appeared in Procurement and Process Communication

In most cases no. tert-Butanol melting point near 25°C, slightly lower temperature may crystallize.

In many scenes, pure phase change does not equal quality change. Key lies in: whether melting process introduces water or pollution, and whether complete full mixing and consistent sampling.

Materials generally describe its compatibility with water strong, commodity info also often writes “miscible with water”.
But in complex system containing salt, multi-component organics, final phase behavior still suggest confirming through pilot test.

Its boiling point in 80+ degrees, and has certain vapor pressure at room temperature.
Whether “obvious” depends on ventilation, opening area and operation method. Controlling actions like pouring, opening lid, agitation well, effect is often more obvious than simply changing solvent.

If local temperature lower than its melting point vicinity, indeed exists possibility of solidification leading to fluidity drop.
Solution idea usually is: Temperature control, insulation, key point heat tracing, and writing rewarming and start-up steps clearly in SOP.

First ask yourself a question: What do you fear most?
If fear “main content not enough”, many grades can satisfy;
If fear “water or certain impurity cause fluctuation”, usually need clearer water and impurity control;
If fear “inter-batch difference”, need to focus on supply stability and trend data, not just single report.

Commonly include: Technical Data Sheet (TDS), Safety Data Sheet (SDS), Certificate of Analysis (COA). For projects with extra control items, can also increase detection items according to agreement.

It belongs to flammable solvent, meanwhile exists feature of solidifying near room temperature.
So packaging choice usually needs to consider simultaneously: sealing, anti-static, temperature control convenience, site drum opening frequency and pollution risk.

We recommend two things most:
Use your real process condition to do a round of “pilot – semi-works” verification (including low temperature state and sampling consistency);
Turn key indicators (e.g. water, color, non-volatile residue, specific impurity) into traceable trend, not just looking at “Qualified/Unqualified”.

Possible, but not suggest direct replacement. Safer way is to put it as candidate solvent into test matrix: run out compatibility, drying performance, residue risk, crystallization behavior with several groups of ratios, then decide whether to replace or blend.

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References & Data Sources

  • 1. Product Identification & Basic Information
    PubChem Compound Summary: tert-Butyl Alcohol. National Library of Medicine (NIH). [Link]
  • 2. Physicochemical Properties
    NIST Chemistry WebBook: tert-Butanol. National Institute of Standards and Technology (NIST). [Link]
  • 3. Toxicological Profile
    IRIS Toxicological Review of tert-Butyl Alcohol (tert-Butanol). Environmental Protection Agency (EPA). [Link]
  • 4. Research & Synthetic Applications
    Selective radical-type perfluoro-tert-butylation of unsaturated compounds with a stable and scalable reagent. Nature Publishing Group. [Link]
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