Fluorides acids

Fmoc-amino acid fluorides have proved to be extremely effective tools for the preparation of peptides containing contiguous iV-alkyl and a,a-disubstituted amino acid residues (43,47,48). 

Weigh out into a dry glass vial Fmoc-amino acid (5 eq) and TFFH (4.9 eq). 

Transfer 10 mg of resin with a wide-mouthed Pasteur pipette to a small, sintered glass funnel. Wash and dry-down as described in Protocol 1C. Perform Kaiser or TNBS test Protocol 13). If positive, repeat steps 5-6. 

If resin still gives a positive colour test after 4 h, wash resin with DMF (5 times) and repeat coupling reaction with fresh reagents. 

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These studies at the same time aroused my interest in the mechanistic aspects of the reaetions, including the complexes of RCOF and RF with BF3 (and eventually with other Lewis acid fluorides) as well as the complexes they formed with aromatics. 1 isolated for the first time at low temperatures arenium tetrafluoroborates (the elusive (T-complexes of aromatic substitutions), although I had no means to pursue their structural study. Thus my long fascination with the chemistry of car-bocationic complexes began. 

Nitronium tetrafluoroborate was first prepared by adding a mixture of anhydrous hydrofluoric acid and boron trifluoride to a solution of dinitrogen pentoxide in nitromethane. Nitric acid can be used in place of dinitrogen pentoxide, and by replacing boron trifluoride by other Lewis-acid fluorides Olah and his co-workers prepared an extensive series of stable nitronium salts. ... 

The carbonylation of aryl halides under mild conditions in the presence of CsF afford.s the acid fluoride 490 in good yields. Unlike acyl chlorides, acyl fluorides are inert toward Pd(0) catalyst[345]. Benzenesulfonyl chloride (491) undergoes desulfonylation-carbonylation to give the benzoate 492 in the presence of titanium tetralkoxide at 160 °C[346]. 

Acid chlorides —COCI Saturated 1815-1790 Acid fluorides higher, bromides and iodides... 

Ammonia. Ammonia (qv) reacts with excess fluorine ia the vapor phase to produce N2, NF, N2F2, HF, and NH F. This reaction is difficult to control ia the vapor phase because of the iatense heat of reaction, and ia some cases only N2 and HF are produced. Nitrogen trifluoride was obtained ia 6% yields ia a gas-phase reaction over copper (42). Yields of ca 60% are achieved by the reaction of fluorine and ammonia ia a molten ammonium acid fluoride solution (43,44). 

Fluorine reacts with ammonia in the presence of ammonium acid fluoride to give nitrogen trifluoride, NF. This compound can be used as a fluorine source in the high power hydrogen fluoride—deuterium fluoride (HF/DF) chemical lasers and in the production of microelectronic siUcon-based components. 

Chloride. Chloride is known to significantly increase the rate of corrosion in acidic fluoride media. The level of chloride that can be tolerated in the HF process before corrosion hinders plant operation is quite low. 

Manufacture and Economics. Nitrogen tritiuoride can be formed from a wide variety of chemical reactions. Only two processes have been technically and economically feasible for large-scale production the electrolysis of molten ammonium acid fluoride and the direct fluorination of the ammonia in the presence of molten ammonium fluoride. In the electrolytic process, NF is produced at the anode and H2 is produced at the cathode. In a divided cell of 4 kA having nickel anodes, extensive dilution of the gas streams with N2 was used to prevent explosive reactions between NF and H2 (17). 

In the direct process, NF is produced by the reaction of NH and F2 in the presence of molten ammonium acid fluoride (27). The process uses a specially designed reactor (28). Because H2 is not generated in this process, the ha2ards associated with the reactions between NF and H2 are elirninated. 

Properties. Other names for potassium bifluoride are potassium hydrogen difluoride and potassium acid fluoride. This white crystalline salt is a soft, waxy soHd. The crystal forms of potassium bifluoride are tetragonal and cubic (21). The bifluoride ion in KHF2 averages 0.2292 nm between fluoride... 

Hexafluoropropylene Oxide HFPO is the most important of the perfluoroepoxides and has been synthesized by almost all of the methods noted. Many attempts have been made to polymerize HFPO (6,8). The most successful has been the reaction of HFPO with fluoride ion at low temperature to give a series of oligomeric acid fluorides which have been end capped to yield stable fluids (eq. 11, where X = H,F). 

Perfluorinated acid fluorides containing heteratoms are also accessible by ECF. Long-chain perfluorinated acid fluorides produced by ECF containing nitrogen (10—12), oxygen (13), and sulfur (14,15) have been reported. The fluorinated mixed sulfonic acid—carboxyflc acid precursors are also known. ECF of hydrocarbon sultones has led to formation of FS02(CF2) C0F, where n = 2,3 (16). 

Fluorinated ether-containing dicarboxyhc acids have been prepared by direct fluorination of the corresponding hydrocarbon (17), photooxidation of tetrafluoroethylene, or by fluoride ion-cataly2ed reaction of a diacid fluoride such as oxalyl or tetrafluorosuccinyl fluorides with hexafluoropropylene oxide (46,47). Equation 8 shows the reaction of oxalyl fluoride with HEPO. A difunctional ether-containing acid fluoride derived from HEPO contains regular repeat units of perfluoroisopropoxy group and is terminated by two alpha-branched carboxylates. 

Reactions Involving the Trifluoromethyl Group. Aluminum chloride effects chlorinolysis of ben2otrifluoride to give ben2otrichloride (307). High yields of volatile acid fluorides are formed from ben2otrifluoride and perfluorocarboxyUc acids (308). 

Titanium corrodes very rapidly in acid fluoride environments. It is attacked in boiling HCl or H2SO4 at acid concentrations of >1% or in ca 10 wt % acid concentration at room temperature. Titanium is also attacked by hot caustic solutions, phosphoric acid solutions (concentrations >25 wt%), boiling AlCl (concentrations >10 wt %), dry chlorine gas, anhydrous ammonia above 150°C, and dry hydrogen—dihydrogen sulfide above 150°C. 

It can be cleaved with mild acid, fluoride ion, or base. ... 

The r-Bumeoc adduct is prepared from the acid fluoride or the mixed carbonate in dioxane, H2O, NaOH. 

Hot oleum (>50°C), strong alkalis, fluoride solutions, sulphur trioxide Strong alkalis, especially >54°C, distilled water >82°C, hydrofluoric acid, acid fluorides, hot concentrated phosphoric acid, lithium compounds >1 77°C, severe shock or impact applications Strong oxidizers, very strong solvents... 

Chemical Designatioiis - Synonyms Acid Ammonium Fluoride, Ammonium Acid Fluoride, Ammonium Hydrogen Fluoride Chemical Formula NH NF. ... 

A particularly important process for the synth sis of jluorinated monomers is attack of functionalized perfluoroalkoxides onto hexafluoropropylene oxide [271, 272, 273, 274] (equation 60) or other fluorinated epoxides [275, 276], resulting in ring-opening ol the epoxide and formation of a new perfluoroalkoxide or acid fluoride... 

Carbon and fluorine can be added to carbon-nitrogen multiple bonds, generally in highly fluorinated substrates. Perfluoromethanimine adds fluoride ion to give perfluoromethanamiiie ion, which will react with acid fluorides or with another... 

During electrochemical fluorination retention of important functional groups or atoms in molecules is essential. Acyl fluorides and chlorides, but not carboxylic acids and anhydrides (which decarboxylate), survive perfluorination to the perfluorinated acid fluorides, albeit with some cyclization in longer chain (>C4) species [73]. Electrochemical fluorination of acetyl fluoride produces perfluoro-acetyl fluoride in 36-45% yields [85]. Electrochemical fluorination of octanoyl chloride results in perfluorinated cyclic ethers as well as perfluorinated octanoyl fluonde. Cyclization decreases as initial substrate concentration increases and has been linked to hydrogen-bonded onium polycations [73]. Cyclization is a common phenomenon involving longer (>C4) and branched chains. a-Alkyl-substituted carboxylic acid chlorides, fluorides, and methyl esters produce both the perfluorinated cyclic five- and six-membered ring ethers as well as the perfluorinated acid... 

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