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Hydroxides and bases

Cesium hydroxide

Also known as Caesium hydroxide, Cesium hydroxide (Cs(OH)), Cesium hydroxide dimer

CAS 21351-79-1Formula HCsOMolar mass 149.91 g/molEC 244-344-1
GHS signal word: Danger. Pictograms: Corrosive, Harmful or irritant, Serious health hazard 9 suppliers listed
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Cesium hydroxide chemical structure, HCsO, CAS 21351-79-1
2D chemical structure

Key facts

What buyers check first

All properties
Appearance
White-yellow hygroscopic crystals
Melting point
342.3 °C
Density
3.68 g/cm³
Solubility
Soluble in about 25 parts water, much heat being evolved
HS code
282590
Category
Hydroxides and bases
UN number
UN 2682
Illustrative photo, colourless crystals in an open woven sack in a warehouse
Typical packagingIllustrative packaging image, not the actual product

What is Cesium hydroxide?

Plain description, key identifiers and synonyms

Caesium hydroxide is an alkali metal hydroxide and a caesium molecular entity.

Identifiers

Registry numbers, names and line notations, tap to copy

IUPAC name
cesium hydroxide
CAS number
21351-79-1 CAS number cross-checkedOther or deprecated CAS: 12182-83-1, 35103-79-8
EC number
244-344-1
Molecular formula
HCsO
UNII
458ZFZ6235
MDL number
MFCD00010964
InChIKey
HUCVOHYBFXVBRW-UHFFFAOYSA-M
InChI
InChI=1S/Cs.H2O/h;1H2/q+1;/p-1
SMILES (canonical and isomeric)
[OH-].[Cs+]

Synonyms

  • Caesium hydroxide
  • Cesium hydroxide (Cs(OH))
  • Cesium hydroxide dimer
  • Caesium hydrate
  • Cesium hydroxide (ACGIH)
  • Cesium hydroxide, monohydrate
  • Cesium hydrate
  • cesium, hydroxide
  • CsOH
  • Cesium, di-mu-hydroxydi-
  • Caesium hydroxide [UN2682] [Corrosive]
  • Caesium hydroxide solution
  • Cesium Hydroxide, 50% Aqueous
  • Cesium hydroxide, 99.9%
  • Cesium hydroxide - 50% aqueous solution
  • Cesium hydroxide monohydrate, technical grade
  • Cesium hydroxide solution, 50 wt. % in H2O
  • Cesium hydroxide monohydrate, 99.95% trace metals basis
  • Cesium hydroxide monohydrate, >=99.5% trace metals basis

Physical and chemical properties

Measured values and descriptors computed from the structure

Physical and chemical properties

Measured values, check the supplier specification for your grade

Appearance
White-yellow hygroscopic crystalsexp.
Melting point
342.3 °Cexp.
Density
3.68 g/cm³exp.
Solubility
Soluble in about 25 parts water, much heat being evolvedexp.
Vapour pressure
0 mmHg (approx)exp.

Values vary by grade. Ask suppliers for the COA or TDS of the batch you buy.

Computed descriptors

Calculated from the structure, useful for screening and formulation

Molecular weight
149.91 g/molcalc.
Exact mass
149.9082 Dacalc.
LogP (octanol/water)
-3.17calc.
Topological polar surface area
30 Ųcalc.
Hydrogen bond donors
0calc.
Hydrogen bond acceptors
1calc.
Rotatable bonds
0calc.
Heavy atoms
2calc.
Rings
0calc.
Aromatic rings
0calc.
Fraction sp3 carbons
0calc.
Formal charge
0calc.
Stereocentres
0calc.
Components
2calc.

Calculated for screening. Confirm critical figures with the supplier.

Safety and hazards

GHS classification summary, not a safety data sheet

GHS signal word
Danger
GHS05: Corrosive
Corrosive
GHS07: Harmful or irritant
Harmful or irritant
GHS08: Serious health hazard
Serious health hazard

Hazard statements

  • H302Harmful if swallowed.
  • H314Causes severe skin burns and eye damage.
  • H318Causes serious eye damage.
  • H361Suspected of damaging fertility or the unborn child.
  • H361fSuspected of damaging fertility.
  • H373May cause damage to organs through prolonged or repeated exposure.
Precautionary statements (20)
  • P203Obtain, read and follow all safety instructions before use.
  • P260Do not breathe dust, fume, gas, mist, vapours or spray.
  • P264Wash skin thoroughly after handling.
  • P264 + P265Wash skin thoroughly after handling. Do not touch eyes.
  • P270Do not eat, drink or smoke when using this product.
  • P280Wear protective gloves, protective clothing, eye protection and face protection.
  • P301 + P317If swallowed: Get medical help.
  • P301 + P330 + P331If swallowed: Rinse mouth. Do not induce vomiting.
  • P302 + P361 + P354If on skin: Take off immediately all contaminated clothing. Immediately rinse with water for several minutes.
  • P304 + P340If inhaled: Remove person to fresh air and keep comfortable for breathing.
  • P305 + P354 + P338If in eyes: Immediately rinse with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P316Get emergency medical help immediately.
  • P317Get medical help.
  • P318If exposed or concerned, get medical advice.
  • P319Get medical help if you feel unwell.
  • P321Specific treatment (see supplemental first aid instructions on the label).
  • P330Rinse mouth.
  • P363Wash contaminated clothing before reuse.
  • P405Store locked up.
  • P501Dispose of contents and container in accordance with local regulations.
UN number
UN 2682
Transport hazard class
8
Packing group
II

GHS classification summary, not a safety data sheet (SDS). Classifications can differ by supplier, grade and concentration. Always check the supplier's SDS.

Full safety data and first aid

Cesium hydroxide suppliers

Sponsored listings first, then the documented ranking: membership, verification, replies, completeness, freshness and ratings

All 9 suppliers
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Where suppliers are based

9 suppliers in 4 countries

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Cesium hydroxide price

Indicative price range per kg from live supplier offers

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Uses and applications

What the substance is used for, by industry and function

Polyols are important raw materials for the production of polyurethane foams. Their synthesis profits from use of cesium hydroxide as base catalyst. In polyol synthesis isomerization of the starting material propylene oxide is an adverse side reaction eventually leading to chain termination in the polymerization with polyisocyanate. The tendency of polyols to undergo isomerization is minimized when using cesium hydroxide, as isomerization tendency decreases in the order Li > Na > K > Rb > Cs.

Recommended as electrolyte in alkaline storage batteries at subzero temperatures, polymerization catalyst for siloxanes.

Industrial uses: Intermediate.

How it is made

Alkaline decomposition can be carried out either by mixing (powdered pollucite) ore with lime and calcium chloride and heating to 800 - 900 °C followed by leaching of the residue or by heating pollucite with sodium chloride and soda ash to 600 - 800 °C followed by leaching. Both processes furnish impure solutions of cesium chloride. Hydrothermal alkaline leaching with Ca(OH)2 at 200 - 280 °C under high pressure has been developed as an industrial process to yield a low-purity cesium hydroxide directly from pollucite.

By adding barium hydroxide to an aqueous solution of cesium sulfate.

Regulatory status

Inventories, regulations and trade controls that list this substance

United States

  • TSCA inventory (USA)
    Status: Active in US commerce

HS code and trade data

Customs classification and reported world trade statistics

Global trade

World import and export statistics for the HS code Cesium hydroxide is traded under.

HS 2825.90Indicative HS code

Inorganic bases not elsewhere classified in heading 2825

World exports in 2024
$972M
+5.4% vs 2023, imports $3.4B
2019 to 2024
Top exporters
  1. China28.5%
  2. United States23.7%
  3. Brazil10.8%
Top importers
  1. South Korea77.2%
  2. Japan4.3%
  3. United States3.8%
Reported customs values in USD, not prices.Full trade data

The HS code shown for Cesium hydroxide is indicative (it was assigned by structure rules). Confirm the classification with your customs broker before shipping.

Frequently asked questions

Quick answers about Cesium hydroxide, based on the data on this page

What is Cesium hydroxide?

Caesium hydroxide is an alkali metal hydroxide and a caesium molecular entity.

What is the CAS number of Cesium hydroxide?

The CAS registry number of Cesium hydroxide is 21351-79-1. Other or deprecated CAS numbers: 12182-83-1, 35103-79-8.

What is the molecular formula and weight of Cesium hydroxide?

The molecular formula of Cesium hydroxide is HCsO and its molar mass is 149.91 g/mol.

What is Cesium hydroxide used for?

Polyols are important raw materials for the production of polyurethane foams. Their synthesis profits from use of cesium hydroxide as base catalyst.

Is Cesium hydroxide hazardous?

Cesium hydroxide carries the GHS signal word "Danger". Main hazards: harmful if swallowed, causes severe skin burns and eye damage, causes serious eye damage. This summary is not an SDS, always read the supplier safety data sheet.

What is the HS code of Cesium hydroxide?

Cesium hydroxide is usually classified under HS code 282590 (Hydrazine and hydroxylamine and their inorganic salts, other inorganic bases, other…). This is indicative, confirm it with your customs broker before shipping.

Where can I buy Cesium hydroxide?

CompoundList lists 9 suppliers of Cesium hydroxide in United States, China, United Kingdom and Indonesia. Send one free request to get and compare quotes. Your contact details stay private until you accept a quote.

What is the price of Cesium hydroxide?

Suppliers quote Cesium hydroxide on request because prices depend on grade, purity, quantity and destination. A free request on CompoundList gets you several quotes to compare.

Guides for buyers

Practical guides that help when you source, ship or handle Cesium hydroxide

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Data last updated 7 Oct 2026. Details may have changed, please confirm them with the supplier. Report an error on this page
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