Benzilic Acid = Diphenyl glycolic acid = Hydroxydiphenyl acetic acid

CAS Number: 76-93-7
Molecular Formula:C14H12O3
EC Number: 200-993-2
Formula Weight:228.25

Benzilic acid is an organic compound with formula C14H12O3 or (C6H5)2(HO)C(COOH). 
Benzilic acid is a white crystalline aromatic acid, soluble in many primary alcohols.
Benzilic Acid, also known as Diphenyl glycolic acid or Hydroxydiphenyl acetic acid, is used in organic synthesis as a starting point for preparation of glycollate pharmaceuticals. 
Ungraded products supplied by Spectrum are indicative of a grade suitable for general industrial use or research purposes and typically are not suitable for human consumption or therapeutic use.

Uses of Benzilic acid:
Benzilic acid is used in the manufacture of glycollate pharmaceuticals including clidinium, dilantin, flutropium, and mepenzolate which are antagonists of the muscarinic acetylcholine receptors.
Benzilic acid is used in manufacture of the incapacitating agent 3-quinuclidinyl benzilate (BZ) and is regulated by the Chemical Weapons Convention. 
Benzilic acid is also monitored by law enforcement agencies of many countries, because of its use in the manufacture in hallucinogenic drugs.
Use: Benzilic Acid is an impurity of Trospium. 
Trospium is a derivative of tropine with anticholinergic property, which is used in the treatment of urinary incontinence as an antispasmodic.

Chemical Properties of Benzilic acid
Benzilic acids form is white powder
A white crystalline aromatic acid soluble in many primary alcohols, which can be prepared by heating a mixture of benzil, alcohol, and potassium hydroxide.

Uses of Benzilic acid
Benzilic Acid is an impurity of Trospium (T892800), a tropine derivative with anticholinergic activity and a antiispasmodic agent.

Preparation of Benzilic acid
Benzilic acid can be prepared by a heating mixture of benzil, ethanol ,and potassium hydroxide.
Another preparation, performed by Liebig in 1838, is the dimerization of benzaldehyde, to benzil, which is transformed to the product by the benzilic acid rearrangement reaction.

The benzilic acid rearrangement takes place with a yield greater than 90% for benzil itself and with lesser yields for substituted benzils, depending upon the kind and number of groups. 
In several cases where the substitute groups were in the ortho-positions to the carbonyl groups, the rearrangement proceeds with yields of 60% to 70%, for instance, o-tolil and mesityl phenyl diketone. nesitil was found to he hindered greatly enough that no detectable rearrangement takes place. 
The purpose of this work was to locate the point beyond which the rearrangement no longer takes place because of steric hindrance. 
The plan was to increase the hindrance gradually until the rearrangement was prevented; the reaction was carried out using three hindered diketones.

Synonyms: Diphenylglycolic acid, Benzilic acid
Linear Formula: (C6H5)2C(OH)COOH
CAS Number: 76-93-7
Molecular Weight: 228.24

Preferred IUPAC name
Hydroxydi(phenyl)acetic acid[1]
Systematic IUPAC name
Hydroxydiphenylethanoic acid

Benzilic acid is a white crystalline aromatic acid soluble in many primary alcohols. 
Benzilic acid can be prepared by heating mixture of benzil, alcohol and potassium hydroxide. 
The other preparation way is through benzaldehyde, which dimerizates to benzil and it is further transformed by benzilic acid rearrangement to benzilic acid. 
This reaction was also the first example of benzilic acid rearrangement preformed by Liebig in 1838.

Other names
α,α-Diphenyl-α-hydroxyacetic acid
α,α-Diphenylglycolic acid
α-Hydroxydiphenyl acetic acid
2,2-Diphenyl-2-hydroxyacetic acid
2-Hydroxy-2,2-diphenylacetic acid
Diphenyl glycolic acid
Hydroxydiphenyl acetic acid

Principle: In the first step alcohol group of benzoin is oxidized to ketone group forming benzil in presence of concentrated nitric acid.
Nitration of aromatic ring is not occurring as sulphuric acid is totally absent in the whole process. 
In the second step on treatment with hydroxide ion molecular rearrangement occurs to 1,2-diketone forming potassium salt of α-hydroxy acid which on acidification yield α-hydroxy acid (benzilic acid).
CAS No.76-93-7
Chemical Name:Benzilic acid

DIPHENYLGLYCOLIC ACID;DiphenylglycollicacidTrospium EP Impurity A;BENZILIC ACID extrapure

Molecular Formula:C14H12O3
Formula Weight:228.25

Diphenylglycolic acid
2-Hydroxy-2,2-diphenylacetic acid
Benzylic acid
hydroxy(diphenyl)acetic acid
Diphenylhydroxyacetic acid
Glycolic acid, diphenyl-
Hydroxydiphenylacetic acid
Acide diphenylhydroxyacetique
alpha-Hydroxy-2,2-diphenylacetic acid
2,2-Diphenyl-2-hydroxyacetic acid
alpha-Hydroxy-alpha-phenylbenzeneacetic acid
NSC 2830

Since its discovery the Benzilic acid rearrangement has been the subject of a number of mechanistic studies and successfully employed in key steps in the synthesis of a number of important target molecules. 
In this review we look at the advances that have been made over the last 20 years in understanding the mechanism of this rearrangement (including the stereochemical aspects), whilst reviewing some important syntheses where this particular rearrangement was used as a key step.

benzeneacetic acid, a-hydroxy-a-phenyl-
benzylic acid
2,2- diphenyl-2-hydroxyacetic acid
a,a- diphenyl-a-hydroxyacetic acid
diphenylglycolic Acid
a,a- diphenylglycolic acid
diphenylhydroxyacetic acid
glycolic acid, diphenyl-
2- hydroxy-2,2-diphenylacetic acid
a- hydroxy-2,2-diphenylacetic acid
2- hydroxy-2,2-diphenylaceticacid
a- hydroxy-a-phenylbenzeneacetic acid
hydroxy(diphenyl)acetic acid
hydroxydiphenylacetic acid
a- hydroxydiphenylacetic acid
a- phenylmandelic acid

General advice
Consult a physician. Show this safety data sheet to the doctor in attendance.
Move out of dangerous area.

If inhaled
If breathed in, move person into fresh air. 
If not breathing, give artificial respiration. Consult a physician.

In case of skin contact
Wash off with soap and plenty of water. Consult a physician.

In case of eye contact
Flush eyes with water as a precaution.

If swallowed
Never give anything by mouth to an unconscious person. 
Rinse mouth with water. Consult a physician.

CAS Number: 76-93-7 check
Beilstein Reference    521402
CHEBI:39414 check
ChEMBL: ChEMBL578171 check
ChemSpider: 6220 
ECHA InfoCard: 100.000.904 
EC Number: 200-993-2
Gmelin Reference: 281752
PubChem CID: 6463
CompTox Dashboard (EPA): DTXSID0058805

Synthesis Reference(s)
The Journal of Organic Chemistry, 29, p. 1631, 1964 DOI: 10.1021/jo01029a509

Safety Profile
Moderately toxic by subcutaneousroute. 
Slightly toxic by ingestion. 
When heated todecomposition it emits acrid smoke and irritating vapors.

Purification Methods
Crystallise benzilic acid from *benzene (ca 6mL/g), or hot H2O.

Benzeneacetic acid, .alpha.-hydroxy-.alpha.-phenyl-
alpha-phenylmandelic acid
Mandelic acid, .alpha.-phenyl-
alpha,alpha-Diphenylglycolic acid
Benzeneacetic acid, alpha-hydroxy-alpha-phenyl-
.alpha.,.alpha.-Diphenylglycolic acid
.alpha.-Hydroxy-2,2-diphenylacetic acid
alpha,alpha-Diphenyl-alpha-hydroxyacetic acid
.alpha.,.alpha.-Diphenyl-.alpha.-hydroxyacetic acid
Mandelic acid, alpha-phenyl-
EINECS 200-993-2
Acide diphenylhydroxyacetique [French]
BRN 0521402
Benzillic acid
HSDB 7709

For most of the experiments we have performed this semester, we have set out to convert one chemical into another with various different methods. 
For a synthetic organic chemist the product of one reaction is often used as the reactant in another.  
This is also the situation that occurs in biochemistry where different chemical pathways use a newly synthesized product to be a reactant for the next reaction in that pathway.  
This is particularly important for the current experiment because the first chemical transformation occurs using a vitamin as the "co-enzyme" for the synthesis of benzoin. 
While enzymes are normally considered to the biological catalysts in cells, Benzilic acid is often a co-enzyme, derived from a vitamin, that actually performs the biochemical transformation. 
Thiamine, vitamin B1, will be used in the current experiment to convert benzaldehyde into benzoin.  

The benzoin produced in the first experiment will then be used in the second to produce benzil.  
Likewise, the benzil will then be used to synthesize benzilic acid. 
Hence, a multi-step synthesis of different compounds. 
These new compounds can then be used in various different applications, some of which are for medicinal purposed.  
The student can research their ultimate uses to observe that no chemical synthesis is for naught. 
The last experiment requires the student to devise a method to convert benzaldehyde into benzoic acid, perhaps employing oxidation methods used previously, or use a method that might be new to the student, even something not previously discussed during lecture or lab. 
Therefore, to provide a variety of methods for producing benzoic acid, students should work independently, examining general oxidation methods for converting aldehydes into acids obtained searching the chemical literature.

Chemical formula: C14H12O3
Molar mass: 228.247 g·mol−1
Appearance: white solid
Density: 1.08 g/cm3
Melting point: 150 to 152 °C (302 to 306 °F; 423 to 425 K)
Boiling point: 180 °C (356 °F; 453 K) (17.3 hPa)
Solubility in water: 2 g/l (20 °C)

Reaction mechanism
The reaction is a representative of 1,2-rearrangements. 
The long-established reaction mechanism was first proposed in its entirety by Christopher Kelk Ingold, and has been updated with in silico data as outlined below. 
The reaction is second order overall in terms of rate, being first order in diketone and first order in base.
A hydroxide anion attacks one of the ketone groups in 1 in a nucleophilic addition to form the alkoxide . 
The next step requires a bond rotation to conformer 3 which places the migrating group R in position for attack on the second carbonyl group. 
In a concerted step, the migrating R group attacks the α-carbonyl group forming another alkoxide with concomitant formation of a keto-group at the other carbon. 
This migration step is rate-determining. 
This sequence resembles a nucleophilic acyl substitution. 
Calculations show that when R is methyl the charge build-up on this group in the transition state can be as high as 0.22 and that the methyl group is positioned between the central carbon carbon bond!

Quality Level: 100
assay: ≥99%
mp: 149-151 °C (lit.)
SMILES string: OC(=O)C(O)(c1ccccc1)c2ccccc2
InChI: 1S/C14H12O3/c15-13(16)14(17,11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10,17H,(H,15,16)

The benzilic acid rearrangement is formally the 1,2-rearrangement of 1,2-diketones to form α-hydroxy–carboxylic acids using a base. 
This reaction receives its name from the reaction of benzil with potassium hydroxide to form benzilic acid. 
First performed by Justus von Liebig in 1838, Benzilic acid is the first reported example of a rearrangement reaction.
Benzilic acid has become a classic reaction in organic synthesis and has been reviewed many times before.
Benzilic acid can be viewed as an intramolecular disproportionation reaction, as one carbon center is oxidized while the other is reduced.

The reaction has been shown to work in aromatic, semi-aromatic, aliphatic, and heterocyclic substrates. 
The reaction works best when the ketone functional groups have no adjacent enolizable protons, as this allows aldol condensation to compete. 
The reaction is formally a ring contraction when used on cyclic diketones. 
Benzilic acid has been found that aryl groups more readily migrate than alkyl groups, and that aryl groups with electron-withdrawing groups migrate the fastest.

Appearance: white to tan powder (est)
Assay: 95.00 to 100.00
Food Chemicals Codex Listed:    No
Melting Point: 151.00 °C. @ 760.00 mm Hg
Boiling Point: 409.00 °C. @ 760.00 mm Hg (est)
Vapor Pressure: 2.320000 mmHg @ 25.00 °C. (est)
Flash Point: 420.00 °F. TCC ( 215.30 °C. ) (est)
logP (o/w): 2.300

The carboxylic acid in intermediate is less basic than the alkoxide and therefore reversible proton transfer takes place favoring intermediate which is protonated on acidic workup to the final α-hydroxy–carboxylic acid. 
Calculations show that an accurate description of the reaction sequence is possible with the participation of water molecules taking responsibility for the stabilization of charge buildup. 
They also provide a shuttle for the efficient transfer of one proton in the formation of intermediate.
The above mechanism is consistent with all available experimental evidence.
The equilibrium between species 1 and 2 is supported by 18O Isotopic labeling experiments. 
In deuterated water, carbonyl oxygen exchange occurs much faster than the rearrangement, indicating that the first equilibrium is not the rate-determining step.
Further experiments showed a larger relative rate in a deuterated solvent system compared to a non-deuterated solvent system of otherwise identical composition. 
This was explained as being due to the greater relative basicity of the deuterated hydroxide anion compared to the normal hydroxide anion, and was used to indicate that hydrogen migration did not occur in the rate determining step of the reaction. 
This ruled out a concerted mechanism for the reaction, as hydrogen transfer would occur in the rate determining step.

Benzilic Acid
Structural Formula Vector Image
Title: Benzilic Acid
CAS Registry Number: 76-93-7
CAS Name: a-Hydroxy-a-phenylbenzeneacetic acid
Additional Names: diphenylglycolic acid
Molecular Formula: C14H12O3
Molecular Weight: 228.24
Percent Composition: C 73.67%, H 5.30%, O 21.03%
Literature References: Prepd from benzil by the action of concd aq or alc KOH: Adams, Marvel, Org. Synth. vol. 1, p 29 (1921); Ballard, Dehn, ibid. coll. vol. I, 82; Kao, Ma, J. Chem. Soc. 1931, 443.
Properties: Monoclinic needles from water. Bitter taste. mp 150°.
Melt is deep red at higher temp. pKa (25°): 3.036. Slightly sol in cold water; freely sol in hot water, alc, ether.
Melting point: mp 150°
pKa: pKa (25°): 3.036
Derivative Type: Potassium salt
Molecular Formula: C14H11O3K
Molecular Weight: 266.33
Percent Composition: C 63.14%, H 4.16%, O 18.02%, K 14.68%
Properties: Crystals, very sol in water, alc.
Derivative Type: Lead salt
Molecular Formula: (C14H11O3)2Pb
Molecular Weight: 661.67
Percent Composition: C 50.83%, H 3.35%, O 14.51%, Pb 31.31%
Properties: Amorphous precipitate. 
Upon heating it becomes a red liquid.
Derivative Type: Methyl ester
Molecular Formula: C15H14O3
Molecular Weight: 242.27
Percent Composition: C 74.36%, H 5.82%, O 19.81%
Properties: mp 74-75°. bp13 187°.
Melting point: mp 74-75°
Boiling point: bp13 187°

Benzilic ester rearrangement
This reaction is identical to the normal benzilic acid rearrangement, except that an alkoxide or an amide anion is used in place of a hydroxide ion. 
The alkoxide used should not be easily oxidizable (such as potassium ethoxide) as this favors the Meerwein–Ponndorf–Verley reduction pathway as a side reaction. 
The reaction is second order overall in terms of rate, being first order in terms of alkoxide and first order in terms of diketone. 
The product of the reaction is an α-hydroxy–ester or an α-hydroxy-amide.

Alpha-ketol rearrangement
The alpha-ketol rearrangement is an interconversion of a hydroxyl alpha to a carbonyl to the complementary carbonyl and hydroxyl groups, with migration of a substituent. 
Benzilic acid is mechanistically equivalent to the benzyllic acid rearrangement at the point after the nucleophile attacks the 1,2-dicarbonyl. 
This variation of the reaction has been known to occur in many substrates bearing the acyloin functional group. 

2,2-Diphenyl-2-hydroxy acetate
Trospium Impuity A
2-hydroxy-2,2-diphenyl-acetic acid
Benzilic acid, >=99%
.alpha.-Hydroxydiphenylacetic acid

Why does benzilic acid only precipitates in acidic solution and why does the pH needs to be < 2 to precipitate the benzilic acid?

Effect of pH on Structure:
The pH of the solution can be used to assess the acidity or alkalinity of a solution. 
The pH of solution is important since the structure of some compounds can be altered at different pH values. 
Some compounds have groups in their structures that can undergo acid-base reactions.

Melting point:149-151 °C(lit.)
Boiling point:180 °C
Density 1.28
refractive index 1.5805 (estimate)
Flash point:180°C/22mm
storage temp. Store below +30°C.
solubility 1.41g/l (experimental)
pkapKa (25°): 3.036
form Powder
color White to cream-white
Water Solubility 1.41 g/L (25 ºC)
Merck 14,1080
BRN 521402
Stability:Stable. Incompatible with strong oxidizing agents. Combustible.
CAS DataBase Reference76-93-7(CAS DataBase Reference)
EWG's Food Scores1
NIST Chemistry ReferenceBenzeneacetic acid, «alpha»-hydroxy-«alpha»-phenyl-(76-93-7)
EPA Substance Registry SystemBenzilic acid (76-93-7)

Benzilic acid was synthesized through a multistep reaction from the starting material of benzaldehyde and through the formations of benzoin and benzil.  
The first reaction produced benzoin by using the thiamine hydrochloride catalyst, followed by an oxidation reaction to produce benzil, and a rearrangement to synthesize benzilic acid.  
By utilizing crystallization, pure solid products of each step were collected and analyzed through IR, NMR spectroscopy, and other physical properties.

About Benzilic acid
Helpful information
Benzilic acid is registered under the REACH Regulation and is manufactured in and / or imported to the European Economic Area, for intermediate use only.
Benzilic acid is used in formulation or re-packing, at industrial sites and in manufacturing.

Consumer Uses of Benzilic acid
ECHA has no public registered data indicating whether or in which chemical products Benzilic acid might be used. 
ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment.

Article service life
ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment. 
ECHA has no public registered data indicating whether or into which articles Benzilic acid might have been processed.

Widespread uses by professional workers
ECHA has no public registered data indicating whether or in which chemical products Benzilic acid might be used. 
ECHA has no public registered data on the types of manufacture using Benzilic acid. 
ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment.

Formulation or re-packing
ECHA has no public registered data indicating whether or in which chemical products Benzilic acid might be used. 
ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment.

Uses at industrial sites
ECHA has no public registered data indicating whether or in which chemical products Benzilic acid might be used. 
ECHA has no public registered data on the types of manufacture using Benzilic acid. 
ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment.

ECHA has no public registered data on the routes by which Benzilic acid is most likely to be released to the environment.

alpha-phenyl-alpha-hydroxyphenylacetic acid
.alpha.-Hydroxy-.alpha.-phenylbenzeneacetic acid
Trospium impurity A, European Pharmacopoeia (EP) Reference Standard
Trospium chloride Related Compound A, United States Pharmacopeia (USP) Reference Standard
Benzilic Acid; Trospium Chloride Related Compound A; Diphenylglycolic Acid; ?-Hydroxy-?-phenylbenzeneacetic Acid; 2,2-Diphenyl-2-hydroxyacetic Acid

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