Iodobenzene Diacetate
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(Diacetoxyiodo)benzene, also known as phenyliodine(III) diacetate (PIDA) is a hypervalent iodine chemical with the formula . It is used as an oxidizing agent in organic chemistry.


Preparation

This reagent was originally prepared by
Conrad Willgerodt Conrad Heinrich Christoph Willgerodt (November 2, 1841 – December 19, 1930) was a German chemist who first described the Willgerodt reaction. Alongside the Willgerodt reaction, he had also discovered Iodosobenzene and chlorobutanol. As for his c ...
by reacting iodobenzene with a mixture of
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
and peracetic acid: :
CHI Chi or CHI may refer to: Greek *Chi (letter), the Greek letter (uppercase Χ, lowercase χ); Chinese *Chi (length), ''Chi'' (length) (尺), a traditional unit of length, about ⅓ meter *Chi (mythology) (螭), a dragon *Chi (surname) (池, pin ...
  +   CHCOH   +   CHCOH   →   CHI(OCCH)   +   HO PIDA can also be prepared from iodosobenzene and glacial acetic acid: : CHIO   +   2  CHCOH   →   CHI(OCCH)   +   HO More recent preparations direct from
iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
, acetic acid, and benzene have been reported, using either sodium perborate or potassium peroxydisulfate as the oxidizing agent: : CH   +   I   +   2  CHCOH   +   KSO   →   CHI(OCCH)   +   KI   +   HSO   +   KHSO The PIDA molecule is termed hypervalent as its iodine atom (technically a hypervalent iodine) is in its +III oxidation state and has more than typical number of
covalent bond A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
s. It adopts a T-shaped molecular geometry, with the phenyl group occupying one of the three equatorial positions of a trigonal bipyramid (
lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...
s occupy the other two) and the axial positions occupied by oxygen atoms from the
acetate An acetate is a salt (chemistry), salt formed by the combination of acetic acid with a base (e.g. Alkali metal, alkaline, Alkaline earth metal, earthy, Transition metal, metallic, nonmetallic or radical Radical (chemistry), base). "Acetate" als ...
groups. The "T" is distorted in that the phenyl-C to I to acetate-O bond angles are less than 90°. A separate investigation of the crystal structure confirmed that it has orthorhombic crystals in space group ''Pnn''2 and reported unit-cell dimensions in good agreement with the original paper. The bond lengths around the iodine atom were 2.08 Å to the phenyl carbon atom and equal 2.156 Å bonds to the acetate oxygen atoms. This second crystal structure determination explained the distortion in the geometry by noting the presence of two weaker intramolecular iodine–oxygen interactions, resulting in an "overall geometry of each iodine hatcan be described as a pentagonal-planar arrangement of three strong and two weak secondary bonds."


Unconventional reactions

One use of PIDA is in the preparation of similar reagents by
substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord for a related one within a chord progression * Substitution (poetry), a variation in poetic scansion * "Substitution" (song), a 2009 song by Silversun Pi ...
of the acetate groups. For example, it can be used to prepare
(bis(trifluoroacetoxy)iodo)benzene (Bis(trifluoroacetoxy)iodo)benzene, , is a hypervalent iodine compound used as a reagent in organic chemistry. It can be used to carry out the Hofmann rearrangement under acidic conditions. Preparation The syntheses of all aryl hypervalent iod ...
(phenyliodine(III) bis(trifluoroacetate), PIFA) by heating in trifluoroacetic acid: PIFA can be used to carry out the Hofmann rearrangement under mildly acidic conditions, rather than the strongly basic conditions traditionally used. The Hofmann decarbonylation of an ''N''-protected asparagine has been demonstrated with PIDA, providing a route to β-amino-L- alanine derivatives. PIDA is also used in Suárez oxidation, where photolysis of hydroxy compounds in the presence of PIDA and iodine generates cyclic ethers. This has been used in several total syntheses, such as the total synthesis of (−)-majucin, (−)-Jiadifenoxolane A, and cephanolide A.


References

{{DEFAULTSORT:Diacetoxyiodo)benzene Reagents for organic chemistry Oxidizing agents Iodanes Acetates Phenyl compounds