Di-tert-butyl dicarbonate

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Di-tert-butyl dicarbonate
Di-tert-butyl-dicarbonate-2D-skeletal.png
Di-tert-butyl-dicarbonate-based-on-similar-xtals-3D-balls.png
Names
Preferred IUPAC name
Di-tert-butyl dicarbonate
Other names
Di-t-butyl pyrocarbonate
Boc anhydride
Boc2O
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.042.021 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 246-240-1
PubChem CID
UNII
  • InChI=1S/C10H18O5/c1-9(2,3)14-7(11)13-8(12)15-10(4,5)6/h1-6H3 Yes check.svgY
    Key: DYHSDKLCOJIUFX-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C10H18O5/c1-9(2,3)14-7(11)13-8(12)15-10(4,5)6/h1-6H3
    Key: DYHSDKLCOJIUFX-UHFFFAOYAG
  • O=C(OC(=O)OC(C)(C)C)OC(C)(C)C
Properties
C10H18O5
Molar mass 218.249 g·mol−1
AppearanceColorless solid or oil
Density 0.95 g·cm3
Melting point 22 to 24 °C (72 to 75 °F; 295 to 297 K)
Boiling point 56 to 57 °C (133 to 135 °F; 329 to 330 K) (0.5 mmHg)
Insoluble
Solubility in other solventsSoluble in most organic solvents
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Very toxic on inhalation T+, LC50 = 100 mg/m3 (4 hr, rat)
Related compounds
Related compounds
Ethyl chloroformate
Phosgene
Diethyl pyrocarbonate
Dimethyl dicarbonate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Di-tert-butyl dicarbonate is a reagent widely used in organic synthesis. [1] Since this compound can be regarded formally as the acid anhydride derived from a tert-butoxycarbonyl (Boc) group, it is commonly referred to as Boc anhydride. This pyrocarbonate reacts with amines to give N-tert-butoxycarbonyl or so-called Boc derivatives. These carbamate derivatives do not behave as amines, which allows certain subsequent transformations to occur that would be incompatible with the amine functional group. The Boc group can later be removed from the amine using moderately strong acids (e.g., trifluoroacetic acid). Thus, Boc serves as a protective group, for instance in solid phase peptide synthesis. Boc-protected amines are unreactive to most bases and nucleophiles, allowing for the use of the fluorenylmethyloxycarbonyl group (Fmoc) as an orthogonal protecting group.

Contents

Preparation

Di-tert-butyl dicarbonate is inexpensive, so it is usually purchased. Classically, this compound is prepared from tert-butanol, carbon dioxide, and phosgene, using DABCO as a base: [2]

Synthesis of Boc anhydride.png

This route is currently employed commercially by manufacturers in China and India. European and Japanese companies use the reaction of sodium tert-butoxide with carbon dioxide, catalysed by p-toluenesulfonic acid or methanesulfonic acid. This process involves a distillation of the crude material yielding a very pure grade.

Boc anhydride is also available as a 70% solution in toluene or THF. As boc anhydride may melt at ambient temperatures, its storage and handling is sometimes simplified by using a solution.

Protection and deprotection of amines

The Boc group can be added to the amine under aqueous conditions using di-tert-butyl dicarbonate in the presence of a base such as sodium bicarbonate. Protection of the amine can also be accomplished in acetonitrile solution using 4-dimethylaminopyridine (DMAP) as the base. [3]

Removal of the Boc in amino acids can be accomplished with strong acids such as trifluoroacetic acid neat or in dichloromethane or with HCl in methanol. [4] [5] [6] A complication may be the tendency of the t-butyl cation intermediate to alkylate other nucleophiles; scavengers such as anisole or thioanisole may be used. [7] [8] Selective cleavage of the N-Boc group in the presence of other protecting groups is possible when using AlCl3.

Reaction with trimethylsilyl iodide in acetonitrile followed by methanol is a mild and versatile method of deprotecting Boc-protected amines. [9] [10] [11] [12]

The use of triethylsilane as a carbocation scavenger in the presence of trifluoroacetic acid in dichloromethane has been shown to lead to increased yields, decreased reaction times, simple work-up and improved selectivity for the deprotection of t-butyl ester and t-butoxycarbonyl sites in protected amino-acids and peptides in the presence of other acid-sensitive protecting groups such as the benzyloxycarbonyl, 9-fluorenylmethoxycarbonyl, O- and S-benzyl and t-butylthio groups. [13]

Other uses

The synthesis of 6-acetyl-1,2,3,4-tetrahydropyridine, an important bread aroma compound, starting from 2-piperidone was accomplished using t-boc anhydride. [14] (See Maillard reaction). The first step in this reaction sequence is the formation of the carbamate from the reaction of the amide nitrogen with boc anhydride in acetonitrile using DMAP as a catalyst.

BOC application.png

Di-tert-butyl dicarbonate also finds applications as a polymer blowing agent due to its decomposition into gaseous products upon heating. [15] [16]

Hazards

Bottles of di-tert-butyl dicarbonate buildup of internal pressure in sealed containers caused by its slow decomposition to di-tert-butyl carbonate and ultimately tert-butanol and CO2 in the presence of moisture. For this reason, it is usually sold and stored in plastic bottles rather than glass ones.

The main hazard of the reagent is its inhalational toxicity. Its median lethal concentration of 100 mg/m3 over 4 hours in rats [17] is comparable to that of phosgene [18] (49 mg/m3 over 50 min in rats).

Related Research Articles

<span class="mw-page-title-main">Protecting group</span> Group of atoms introduced into a compound to prevent subsequent reactions

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis.

<span class="mw-page-title-main">Peptide synthesis</span> Production of peptides

In organic chemistry, peptide synthesis is the production of peptides, compounds where multiple amino acids are linked via amide bonds, also known as peptide bonds. Peptides are chemically synthesized by the condensation reaction of the carboxyl group of one amino acid to the amino group of another. Protecting group strategies are usually necessary to prevent undesirable side reactions with the various amino acid side chains. Chemical peptide synthesis most commonly starts at the carboxyl end of the peptide (C-terminus), and proceeds toward the amino-terminus (N-terminus). Protein biosynthesis in living organisms occurs in the opposite direction.

In chemistry, solid-phase synthesis is a method in which molecules are covalently bound on a solid support material and synthesised step-by-step in a single reaction vessel utilising selective protecting group chemistry. Benefits compared with normal synthesis in a liquid state include:

The Hofmann rearrangement is the organic reaction of a primary amide to a primary amine with one less carbon atom. The reaction involves oxidation of the nitrogen followed by rearrangement of the carbonyl and nitrogen to give an isocyanate intermediate. The reaction can form a wide range of products, including alkyl and aryl amines.

The Gabriel synthesis is a chemical reaction that transforms primary alkyl halides into primary amines. Traditionally, the reaction uses potassium phthalimide. The reaction is named after the German chemist Siegmund Gabriel.

<span class="mw-page-title-main">Trimethylsilyl group</span> Functional group

A trimethylsilyl group (abbreviated TMS) is a functional group in organic chemistry. This group consists of three methyl groups bonded to a silicon atom [−Si(CH3)3], which is in turn bonded to the rest of a molecule. This structural group is characterized by chemical inertness and a large molecular volume, which makes it useful in a number of applications.

<span class="mw-page-title-main">Curtius rearrangement</span> Chemical reaction

The Curtius rearrangement, first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of nucleophiles such as water, alcohols and amines, to yield a primary amine, carbamate or urea derivative respectively. Several reviews have been published.

<span class="mw-page-title-main">Carbonyldiimidazole</span> Chemical compound

1,1'-Carbonyldiimidazole (CDI) is an organic compound with the molecular formula (C3H3N2)2CO. It is a white crystalline solid. It is often used for the coupling of amino acids for peptide synthesis and as a reagent in organic synthesis.

Silyl ethers are a group of chemical compounds which contain a silicon atom covalently bonded to an alkoxy group. The general structure is R1R2R3Si−O−R4 where R4 is an alkyl group or an aryl group. Silyl ethers are usually used as protecting groups for alcohols in organic synthesis. Since R1R2R3 can be combinations of differing groups which can be varied in order to provide a number of silyl ethers, this group of chemical compounds provides a wide spectrum of selectivity for protecting group chemistry. Common silyl ethers are: trimethylsilyl (TMS), tert-butyldiphenylsilyl (TBDPS), tert-butyldimethylsilyl (TBS/TBDMS) and triisopropylsilyl (TIPS). They are particularly useful because they can be installed and removed very selectively under mild conditions.

<span class="mw-page-title-main">Trifluoroacetic acid</span> Chemical compound

Trifluoroacetic acid (TFA) is an organofluorine compound with the chemical formula CF3CO2H. It is a structural analogue of acetic acid with all three of the acetyl group's hydrogen atoms replaced by fluorine atoms and is a colorless liquid with a vinegar-like odor.

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<span class="mw-page-title-main">Holton Taxol total synthesis</span>

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<i>tert</i>-Butyloxycarbonyl protecting group Protecting group used in organic synthesis

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<span class="mw-page-title-main">Trimethylsilyl trifluoromethanesulfonate</span> Chemical compound

Trimethylsilyl trifluoromethanesulfonate (TMSOTf) is an organosilicon compound with the formula (CH3)3SiO3SCF3. It is a colorless moisture-sensitive liquid. It is the trifluoromethanesulfonate derivative of trimethylsilyl. It is mainly used to activate ketones and aldehydes in organic synthesis.

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<span class="mw-page-title-main">Strychnine total synthesis</span>

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<span class="mw-page-title-main">Trimethylsilyl iodide</span> Chemical compound

Trimethylsilyl iodide (iodotrimethylsilane or TMSI) is an organosilicon compound with the chemical formula (CH3)3SiI. It is a colorless, volatile liquid at room temperature.

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Di-tert-butyl-iminodicarboxylate is an organic compound that can be described with the formula [(CH3)3COC(O)]2NH. It is a white solid that is soluble in organic solvents. The compound is used as a reagent for the preparation of primary amines from alkyl halides. It was popularized as an alternative to the Gabriel synthesis for the same conversion. Amines can also be prepared from alcohols by dehydration using the Mitsunobu reaction.

References

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  12. Zhijian Liu; Nobuyoshi Yasuda; Michael Simeone; Robert A. Reamer (2014). "N-Boc Deprotection and Isolation Method for Water-Soluble Zwitterionic Compounds". J. Org. Chem. 79 (23): 11792–11796. doi:10.1021/jo502319z. PMID   25376704.
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  16. Wypych, George (20 February 2017). Handbook of Foaming and Blowing Agents - 1st Edition (1st ed.). ChemTec Publishing. p. 258. ISBN   978-1-895198-99-7 . Retrieved 4 May 2020.
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