Benzophenone Oxime: Properties, Synthesis & Lab Uses

Benzophenone oxime is a crystalline organic compound derived from benzophenone by condensation with hydroxylamine, serving as a versatile intermediate in organic synthesis, a chelating agent for metal ions, and a reference standard in analytical chemistry.

CAS Number

574-66-3

Molecular Formula

C₁₃H₁₁NO

Molecular Weight

197.23 g/mol

Melting Point

approximately 143–144 °C (literature value; verify against CoA)

Appearance

White to off-white crystalline solid

Solubility

Soluble in ethanol, acetone, and diethyl ether; sparingly soluble in water

SKU

B304037

Chemical Identity and Physical Properties

Benzophenone oxime (IUPAC name: diphenylmethanone oxime; CAS 574-66-3) is formed by the nucleophilic addition of hydroxylamine to the carbonyl group of benzophenone, yielding a C=N–OH (oxime) functional group. Its molecular formula is C₁₃H₁₁NO with a molecular weight of 197.23 g/mol.

The compound exists as a white to off-white crystalline solid with a reported melting point in the range of 143–144 °C. Because the C=N bond is geometrically constrained, oximes can in principle exist as E (anti) and Z (syn) geometric isomers; for unsymmetrical ketone oximes both isomers are isolable, but benzophenone oxime, derived from a symmetric diaryl ketone, exists as a single geometric isomer.

Benzophenone oxime is soluble in common polar organic solvents such as ethanol, acetone, and diethyl ether, but has limited solubility in water. Solutions should be stored away from strong acids, which can promote hydrolysis back to benzophenone, and away from strong oxidants.

Synthesis and Key Reactions

Synthesis from benzophenone: The standard laboratory preparation involves refluxing benzophenone with hydroxylamine hydrochloride in the presence of a base (commonly sodium acetate or pyridine) in an aqueous-ethanolic medium. The reaction proceeds via nucleophilic addition of free hydroxylamine to the carbonyl, followed by dehydration to form the oxime. Yields are typically high under mild conditions, and the product is isolated by crystallization.

Beckmann rearrangement: Like other oximes, benzophenone oxime undergoes the Beckmann rearrangement under acidic or Lewis-acid conditions to afford an amide. Because benzophenone oxime is symmetric (both migrating groups are phenyl), the rearrangement yields a single product, benzanilide (N-phenylbenzamide). This reaction is an important textbook example used to illustrate the stereochemical course of the Beckmann rearrangement.

O-functionalization: The oxime hydroxyl can be alkylated or acylated to produce O-alkyl or O-acyl oxime derivatives, which are useful intermediates in heterocyclic synthesis and as photoinitiators.

Reduction: Catalytic or chemical reduction of benzophenone oxime gives benzhydrylamine (diphenylmethylamine), a chiral amine precursor used in asymmetric synthesis.

Laboratory and Industrial Applications

Analytical chelating agent: Benzophenone oxime and related diarylketone oximes have historically been investigated as chelating ligands for transition and heavy metal ions (e.g., Cu²⁺, Ni²⁺, Co²⁺). The oxime N–OH moiety coordinates to metals via the nitrogen and/or oxygen atoms, forming stable complexes useful in gravimetric analysis and solvent extraction of metals.

Synthetic intermediate: As noted above, benzophenone oxime serves as a precursor to benzanilide (via Beckmann rearrangement), benzhydrylamine (via reduction), and diverse O-substituted oxime ethers and esters. These downstream products appear in pharmaceutical, agrochemical, and materials chemistry contexts.

Photoinitiator precursors: O-acyl oximes derived from diaryl ketone oximes are well-established type-II radical photoinitiators widely used in UV-curable coatings, inks, and photoresists. Benzophenone oxime is therefore a relevant synthetic building block in photoinitiator development.

Reference standard and reagent: High-purity benzophenone oxime (such as Aladdin SKU B304037) is used as a reference standard for analytical method development and as a starting material for exploratory chemistry.

Handling, Storage, and Safety Considerations

Benzophenone oxime should be handled in a well-ventilated fume hood with appropriate personal protective equipment, including nitrile gloves, safety glasses, and a laboratory coat. Although it is a solid at room temperature and presents a relatively low acute hazard compared to many reagents, as an oxime it may release small quantities of hydroxylamine or nitrogen oxides upon thermal decomposition; avoid exposure to open flames or excessive heat.

Storage: Store in a tightly sealed container in a cool, dry location away from light, strong acids, and oxidizing agents. Recommended storage temperature is typically ambient (15–25 °C) or as indicated on the product label and Certificate of Analysis (CoA). Under these conditions the compound is stable for extended periods.

Disposal: Dispose of waste material in accordance with local, national, and institutional regulations for organic chemical waste. Do not discharge into drains or waterways.

Always consult the current Safety Data Sheet (SDS) for benzophenone oxime (B304037) before use. Specific hazard classifications, first-aid measures, and regulatory information are detailed therein.

Frequently asked questions

What is the CAS number for benzophenone oxime?

The CAS registry number for benzophenone oxime is 574-66-3. It is also known by the synonyms diphenylmethanone oxime and diphenyl ketone oxime.

How do I prepare benzophenone oxime in the laboratory?

Benzophenone oxime is conveniently prepared by heating benzophenone with hydroxylamine hydrochloride and a base such as sodium acetate in an aqueous-ethanolic solvent. After reflux, the mixture is cooled, and the crystalline product is collected by filtration and recrystallized from ethanol or ethanol-water.

What happens when benzophenone oxime undergoes Beckmann rearrangement?

Because benzophenone is a symmetric diaryl ketone, Beckmann rearrangement of its oxime yields a single amide product: benzanilide (N-phenylbenzamide). This makes benzophenone oxime a useful model substrate for studying and demonstrating the Beckmann rearrangement mechanism.

In what solvents is benzophenone oxime soluble?

Benzophenone oxime dissolves readily in polar organic solvents such as ethanol, acetone, and diethyl ether. It has limited solubility in water and should not be expected to form clear aqueous solutions at practical laboratory concentrations.

What purity grade is Aladdin's benzophenone oxime (B304037) suitable for?

Aladdin offers benzophenone oxime under SKU B304037. For specific purity grade, lot-specific purity data, and analytical certificates, please refer to the current product page or contact Aladdin technical support, as specifications can vary by lot.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 4th ed.; Wiley: New York, 1992. (Beckmann rearrangement and oxime chemistry)
2. Smith, M. B. Organic Synthesis, 4th ed.; Academic Press, 2017. (General oxime synthesis and reactions)
3. Spectroscopic data and physical constants for benzophenone oxime, CAS 574-66-3, as compiled in standard chemical databases (e.g., SDBS, Reaxys, SciFinder).

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