関: benzil、benzylic

WordNet

the univalent radical derived from toluene (同)benzyl_group, benzyl radical
relating to benzyl

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/09/30 17:15:27」(JST)

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(Benzyl group): Benzyl radical, benzyl amine, benzyl bromide, chloroformyl benzoate and benzylmethyl ether. R = heteroatom, alkyl, aryl, allyl etc. or other substituents.

In organic chemistry, benzyl is the substituent or molecular fragment possessing the structure C₆H₅CH₂-. Benzyl features a benzene ring attached to a CH₂ group.^[1]

Nomenclature

In IUPAC nomenclature the prefix benzyl refers to a C₆H₅CH₂ substituent, for example benzyl chloride or benzyl benzoate. Benzyl is not to be confused with phenyl with the formula C₆H₅. The term benzylic is used to describe the position of the first carbon bonded to a benzene or other aromatic ring. For example the molecule, is referred to as a "benzylic" carbocation. The benzyl free radical has the formula C₆H₅CH₂. The benzyl carbocation has the formula C₆H₅CH₂⁺; the carbanion has the formula C₆H₅CH₂⁻. None of these species can be formed in significant amounts under normal conditions, but they are useful referents for discussion of reaction mechanisms.

Abbreviations

The abbreviation "Bn" is frequently used to denote benzyl groups in nomenclature and structural depictions of chemical compounds. For example, benzyl alcohol can be represented as BnOH. This abbreviation is not to be confused with "Bz", which is the abbreviation for the benzoyl group C₆H₅C(O)−, or the phenyl group C₆H₅, abbreviated "Ph".

Reactivity of benzylic centers

The enhanced reactivity of benzylic positions is attributed to the low bond dissociation energy for benzylic C−H bonds. Specifically, the bond C₆H₅CH₂−H is about 10–15% weaker than other kinds of C−H bonds. The neighboring aromatic ring stabilizes benzyl radicals. The data tabulated below compare benzylic C−H bond to related C−H bond strengths.

Bond	Bond	Bond-dissociation energy		Comment
Bond	Bond	(kcal/mol)	(kJ/mol)	Comment
C₆H₅CH₂−H	benzylic C−H bond	90	377	akin to allylic C−H bonds such bonds show enhanced reactivity
H₃C−H	Methyl C−H bond	105	439	One of the strongest aliphatic C−H bonds
C₂H₅−H	Ethyl C−H bond	101	423	slightly weaker than H₃C−H
C₆H₅−H	phenyl C−H bond	113	473	comparable to vinyl radical, rare
CH₂=CHCH₂−H	allylic C–H bond	89	372	such bonds show enhanced reactivity

The weakness of the C−H bond reflects the stability of the benzylic radical. For related reasons, benzylic substituents exhibit enhanced reactivity, as in oxidation, free radical halogenation, or hydrogenolysis. As a practical example, in the presence of suitable catalysts, p-xylene oxidizes exclusively at the benzylic positions to give terephthalic acid:

CH₃C₆H₄CH₃ + 3 O₂ → HO₂CC₆H₄CO₂H + 2 H₂O.

Millions of tonnes of terephthalic acid are produced annually by this method.^[2]

Benzyl protective groups

Benzyl groups are frequently used in organic synthesis as protective group for alcohols and carboxylic acids.

Two common methods for benzyl ether protection:

reaction of alcohol with benzyl bromide and a strong base such as sodium hydride as in a Williamson ether synthesis^[3]
reaction of alcohol with an imidate such as benzyl trichloroacetimidate (C₆H₅CH₂OC(CCl₃)=NH) promoted by trifluoromethanesulfonic acid. An example forming a p-methoxybenzyl (PMB) ether in total synthesis:^[4]

The benzyl group can be removed by hydrogenolysis. PMB ethers can be cleaved by magnesium bromide –dimethyl sulfide, CAN or DDQ.^[5]

One study ^[6] employs a benzyloxy pyridinium salt as a benzyl transfer reagent for alcohols:

Trifluorotoluene was used as the solvent in the presence of magnesium oxide as an acid scavenger. The reaction type for this conversion is believed to be S_N1 based on the detection of trace amounts of Friedel-Crafts reaction side-products with toluene as a solvent.

References

^ Carey, F. A., and Sundberg, R. J.; Advanced Organic Chemistry, Part A: Structure and Mechanisms, 5th ed.; Springer: New York, NY, 2008. pp 806–808, 312–313.
^ Richard J. Sheehan, "Terephthalic Acid, Dimethyl Terephthalate, and Isophthalic Acid" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a26_193
^ DeSelms, R. H.; Benzyl Phenyl Ether Compounds; Enigen Science Publishing: Washington, DC, 2008.^{[dead link]}
^ Total synthesis of rutamycin B via Suzuki macrocyclization James D. White, Thomas Tiller, Yoshihiro Ohba, Warren J. Porter, Randy W. Jackson, Shan Wang, and Roger Hanselmann 80 Chem. Commun., 1998 doi:10.1039/a707251a
^ Protecting groups Krzysztof Jarowicki and Philip Kocienski J. Chem. Soc., Perkin Trans. 1, 1998, 4005–4037 4005 doi:10.1039/a803688h
^ K. W. C. Poon and G. B. Dudley (2006). "Mix-and-Heat Benzylation of Alcohols Using a Bench-Stable Pyridinium Salt". J. Org. Chem. 71 (10): 3923–3927. doi:10.1021/jo0602773. PMID 16674068.

External links

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Quotations related to Benzyl at Wikiquote

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English Journal

Hydrophobic oligopeptide-based star-block copolymers as unimolecular nanocarriers for poorly water-soluble drugs.

Li J, Li J, Xu S, Zhang D, Liu D.SourceMedical College, Shantou University, 22 Xinling Road, Shantou, 515041, PR China.
Colloids and surfaces. B, Biointerfaces.Colloids Surf B Biointerfaces.2013 Oct 1;110:183-90. doi: 10.1016/j.colsurfb.2013.04.049. Epub 2013 May 7.
Hydrophobic oligopeptide (HOP)-based star-block copolymers of the form PEI-g-(HOP-b-PEG) were synthesized, characterized and evaluated as nanocarriers for poorly water-soluble drugs. The designed PEI-g-(HOP-b-PEG) polymers were composed of a hyperbranched polyethylenimine (PEI) core, a HOP [i.e., ol
PMID 23722014

Rapid screening and structural elucidation of a novel sibutramine analogue in a weight loss supplement: 11-Desisobutyl-11-benzylsibutramine.

Mans DJ, Gucinski AC, Dunn JD, Gryniewicz-Ruzicka CM, Mecker-Pogue LC, Kao JL, Ge X.SourceU.S. Food and Drug Administration, CDER Division of Pharmaceutical Analysis, 1114 Market St., St. Louis, MO 63101 United States. Electronic address: Daniel.Mans@fda.hhs.gov.
Journal of pharmaceutical and biomedical analysis.J Pharm Biomed Anal.2013 Sep;83:122-8. doi: 10.1016/j.jpba.2013.02.031. Epub 2013 Feb 28.
A novel analogue of sibutramine, 11-desisobutyl-11-benzylsibutramine, has been discovered. During routine ion mobility spectrometry (IMS) screening of a weight loss supplement collected at an US FDA import operation facility an unknown peak was observed. Further analysis of the supplement by liquid
PMID 23739298

Molecular weight controls the elongation of oblate-shaped degradable poly(γ-benzyl-l-glutamate)nanoparticles.

Cauchois O, Segura-Sanchez F, Ponchel G.SourceUniversité Paris Sud XI, Faculté de Pharmacie, UMR CNRS 8612, 5 rue Jean-Baptiste Clément, Châtenay-Malabry 92210, France. Electronic address: cauchois.olivier@gmail.com.
International journal of pharmaceutics.Int J Pharm.2013 Aug 16;452(1-2):292-9. doi: 10.1016/j.ijpharm.2013.04.074. Epub 2013 May 9.
The shape of nanoparticles in drug targeting applications has been recently suggested as being an interesting parameter for modulating their fate in the body after delivery. In view of investigating the incidence of this parameter on in vivo distribution, poly(γ-benzyl-l-glutamate) (PBLG) has been
PMID 23665007

Japanese Journal

Odd–Even Effect Observed in [Ni(dmit)₂] Complex Salts of Quaternary Ammonium Cation with Both Benzyl Groups and ω-Phenylalkyl Groups

Saeki Masahiro,Dai Kotaro,Ichimura Shuhei [他]
Bulletin of the Chemical Society of Japan 88(2), 358-365, 2015-02
NAID 40020358880

Formation and characterization of a reactive chromium(V)–oxo complex: mechanistic insight into hydrogen-atom transfer reactions

Kotani Hiroaki,Kaida Suzue,Ishizuka Tomoya,Sakaguchi Miyuki,Ogura Takashi,Shiota Yoshihito,Yoshizawa Kazunari,Kojima Takahiko
Chemical science 6(2), 945-955, 2015-02
… When benzyl alcohol derivatives (R-BA) with different oxidation potentials were employed as substrates, corresponding aldehydes were obtained as the 2e−-oxidized products in moderate yields as determined from 1H NMR and GC-MS measurements. …
NAID 120005555645

SYNTHESIS AND CRYSTAL STRUCTURE OF (4S)-4-BENZYL-3-(4,5-DIMETHOXY-2-METHYLBENZOYL)-2,2-DIMETHYL-1,3-OXAZOLIDINE (Dedicated to Professor Isao Kuwajima on the occasion of his 77th birthday)

Chrzanowska Maria,Meissner Zofia,Chrzanowska Joanna M. [他]
Heterocycles : an international journal for reviews and communications in heterocyclic chemistry 90(1), 730-739, 2015-01-01
NAID 40020330673

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★リンクテーブル★

リンク元	「ベンジル」「benzylic」「benzil」
拡張検索	「benzylhydrochlorothiazide」「dibenzylchlorethamine」「3-iodobenzylguanidine」「benzylthiouracil」