Phenylboronic acid or benzeneboronic acid, abbreviated as PhB(OH)₂ where Ph is the phenyl group C₆H₅-, is a

boronic acid A boronic acid is an organic compound related to boric acid () in which one of the three hydroxyl groups () is replaced by an alkyl or aryl group (represented by R in the general formula ). As a compound containing a carbon–boron bond, membe ...

containing a phenyl substituent and two

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydro ...

groups attached to boron. Phenylboronic acid is a white powder and is commonly used in organic synthesis. Boronic acids are mild Lewis acids which are generally stable and easy to handle, making them important to organic synthesis.

Properties

Phenylboronic acid is

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...

in most polar

organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

s and is poorly soluble in

hexane Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14. It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relatively ...

s and carbon tetrachloride. This planar compound has idealized C_2V molecular symmetry. The boron atom is sp²-hybridized and contains an empty

p-orbital In atomic theory and quantum mechanics, an atomic orbital is a function describing the location and wave-like behavior of an electron in an atom. This function can be used to calculate the probability of finding any electron of an atom in any spe ...

. The orthorhombic crystals use hydrogen bonding to form units made up of two molecules. These dimeric units are combined to give an extended hydrogen-bonded network. The molecule is planar with a minor bend around the C-B bond of 6.6° and 21.4° for the two PhB(OH)₂ molecules.Hall, D. G. ''Boronic Acids''; WILEY-VCH: Edmonton, Canada, 2005.

Synthesis

Numerous methods exist to synthesize phenylboronic acid. One of the most common synthesis uses phenylmagnesium bromide and

trimethyl borate Trimethyl borate is the organoboron compound with the formula B(OCH3)3. It is a colourless liquid that burns with a green flame. It is an intermediate in the preparation of sodium borohydride and is a popular reagent in organic chemistry. It is ...

to form the

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...

PhB(OMe)₂, which is then hydrolyzed to the product. :PhMgBr + B(OMe)₃ → PhB(OMe)₂ + MeOMgBr :PhB(OMe)₂ + H₂O → PhB(OH)₂ + MeOH Other routes to phenylboronic acid involve electrophilic borates to trap phenylmetal intermediates from phenyl halides or from directed ortho-

metalation Metalation (Alt. spelling: Metallation) is a chemical reaction that forms a bond to a metal. This reaction usually refers to the replacement of a halogen atom in an organic molecule with a metal atom, resulting in an organometallic compound. In the ...

Phenylsilane Phenylsilane, also known as silylbenzene, a colorless liquid, is one of the simplest organosilanes with the formula C6 H5 SiH3. It is structurally related to toluene, with a silyl group replacing the methyl group. Both of these compounds have ...

s and phenylstannanes transmetalate with BBr₃, followed by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

form phenylboronic acid. Aryl halides or

triflates In organic chemistry, triflate (systematic name: trifluoromethanesulfonate), is a functional group with the formula and structure . The triflate group is often represented by , as opposed to −Tf, which is the triflyl group, . For example, ...

can be coupled with diboronyl reagents using transition metal catalysts. Aromatic C-H functionalization can also be done using transition metal

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

Reactions

The

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

of boronic acids gives

boroxine Boroxine () is a 6-membered heterocyclic compound composed of alternating oxygen and singly-hydrogenated boron atoms. Boroxine Derivative (chemistry), derivatives (boronic anhydrides) such as trimethylboroxine and triphenylboroxine also make up a ...

s, the trimeric

anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...

s of phenylboronic acid. The dehydration reaction is driven thermally, sometimes with a dehydration agent. Triphenyl boroxine synthesis01

Phenylboronic acid participates in numerous cross coupling reactions where it serves as a source of a phenyl group. One example is the

Suzuki reaction The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide and the catalyst is a palladium, palladium(0) complex. It was first published in 1979 by Akira ...

where, in the presence of a Pd(0) catalyst and base, phenylboronic acid and vinyl halides are coupled to produce phenyl

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

s. This method was generalized to a route producing

biaryl Biphenyl (also known as diphenyl, phenylbenzene, 1,1′-biphenyl, lemonene or BP) is an organic compound that forms colorless crystals. Particularly in older literature, compounds containing the functional group consisting of biphenyl less one ...

s by coupling phenylboronic acid with aryl halides. C-C bond forming processes commonly use phenylboronic acid as a reagent. Alpha-amino acids can be generated using the uncatalyzed reaction between

alpha-ketoacid In organic chemistry, keto acids or ketoacids (also called oxo acids or oxoacids) are organic compounds that contain a carboxylic acid group () and a ketone group ().Franz Dietrich Klingler, Wolfgang Ebertz "Oxocarboxylic Acids" in Ullmann's ...

amines In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...

, and phenylboronic acid. Heck-type cross coupling of phenylboronic acid and alkenes and alkynes has been demonstrated. Aryl azides and nitroaromatics can also be generated from phenylboronic acid. Phenylboronic acid can also be regioselectively halodeboronated using aqueous

bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...

chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...

, or iodine: :PhB(OH)₂ + Br₂ + H₂O → PhBr + B(OH)₃ + HBr Boronic esters result from the condensation of boronic acids with alcohols. This transformation is simply the replacement of the hydroxyl group by

alkoxy In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also ...

aryloxy In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus . The range of alkoxy groups is vast, the simplest being methoxy (). An ethoxy group () is found in the organic compound ethyl phenyl ether (, also ...

groups. This

reversible reaction A reversible reaction is a reaction in which the conversion of reactants to products and the conversion of products to reactants occur simultaneously. : \mathit aA + \mathit bB \mathit cC + \mathit dD A and B can react to form C and D or, in the ...

is commonly driven to product by the use of Dean-Stark apparatus or a dehydration agent to remove water. :PhB(OH)₂ + 2 ROH PhB(OR)₂ + 2 H₂O As an extension of this reactivity, PhB(OH)₂ can be used as a protecting group for diols and

diamine A diamine is an amine with exactly two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term ''diamine'' refers mostly to primary diamines, as those are the most reactive. In terms of quantities p ...

s. This reactivity is the basis of the use of phenylboronic acid's use as a receptor and sensor for carbohydrates,

antimicrobial An antimicrobial is an agent that kills microorganisms or stops their growth. Antimicrobial medicines can be grouped according to the microorganisms they act primarily against. For example, antibiotics are used against bacteria, and antifungals ar ...

agents, and

enzyme inhibitor An enzyme inhibitor is a molecule that binds to an enzyme and blocks its activity. Enzymes are proteins that speed up chemical reactions necessary for life, in which substrate molecules are converted into products. An enzyme facilitates a sp ...

neutron capture therapy Neutron capture therapy (NCT) is a type of radiotherapy for treating locally invasive malignant tumors such as primary brain tumors, recurrent cancers of the head and neck region, and cutaneous and extracutaneous melanomas. It is a two-step pro ...

for

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

, transmembrane transport, and bioconjugation and labeling of

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s and cell surface.

Properties

Synthesis

Reactions

See also

References

Further reading