This application is a continuation of application Ser. No. 07/477,523 filed Feb. 9, 1990 now abandoned. 
    
    
     The invention relates to a novel process for the preparation of a ditertiary-alkyl dicarbonate. More particularly, it relates to the preparation of a ditertiary-butyl dicarbonate from an acid halide. 
     BACKGROUND OF THE INVENTION 
     The expression tertiary-alkyl designates a saturated hydrocarbon radical having a tertiary carbon which carries ethyl or methyl radicals independently of one another. If the tertiary carbon carries only methyls, the tertiary-alkyl radical is tertiary-butyl. In the description which follows, only the tertiary-butyl radical will be discussed as an example of the tertiary-alkyls envisaged by the description; however, the use of one example as a means to describe the process is not intended to limit the scope of protection to only one species. 
     It is well known in the art to prepare ditertiary-butyl dicarbonate, (BOC) 2  O, from tertiary-butyl carbonate and phosgene, such as described by J. H. Howe in the Journal of Organic Chemistry 27, 1901 (1962). However, industry avoids the use of phosgene due to safety problems. 
     It is also known to prepare tertiary-butyl dicarbonate by condensing tertiary-butyl carbonate with an acid chloride in a mixture of toluene and dimethylformamide as disclosed by the article published by Pozdev, Smirnova Podgornova, Zentsova and le Kalei in Zhurnal Urganicheskoi Khimii, volume 15, No. 1, pages 106-109, in 1979 and translated in the Journal of Organic Chemistry USSR 1979, page 95. However, when we reproduced these experiments, the yields of tertiary.-butyl dicarbonate obtained were not satisfactory. 
     SUMMARY OF THE INVENTION 
     Applicants have discovered a process for preparing dicarbonate in the absence of phosgene and in good yields. The process comprises condensing tertiary-butyl pyrocarbonate with an acid halide in the presence of a complexing agent. 
     The reaction is represented diagrammatically below: ##STR1## wherein X represents a halogen and M represents an alkali metal. 
     The tertiary-butyl pyrocarbonate is obtained in any known manner, for example by carbonating a tertiary-butylate. The preferred tertiary-butyl pyrocarbonates, are salts of the alkali metals K, Na, Li and most particularly the sodium salt (M=Na). 
     The acid halides which are useful in the process of the invention are selected from the chlorides or bromides of carboxylic acids having 1 to 7 carbon atoms and preferably substituted by electron-attracting groups, such as halogen atoms for the aliphatic and aromatic series, and nitro groups for the aromatic series. 
     Preferred acid halides are carboxylic acid chlorides having 2 carbon atoms. Of these preferred acid halides, trihalogenoacetyl chloride and dihalogenoacetyl chloride are most preferred, the most accessible being dichloroacetyl and trichloroacetyl chlorides. 
     The sequestering agents are selected from at least 3 classes of complexing agents, comprising the oxygen-containing tertiary amines and the oxygen- or sulfur-containing, cyclic or macrocyclic polyethers. 
     The first class consist of sequestering agents of formula I: 
     
         N--[--CHR.sub.1 --CHR.sub.2 --O--(CHR.sub.3 --CHR.sub.4 --O).sub.n --R.sub.5 ].sub.3                                         I 
    
     wherein n is an integer greater than or equal to 0 and smaller than or equal to about 10 (0≦n≦10); R 1 , R 2 , R 3 , and R 4 , which are identical or different, represent a hydrogen atom or an alkyl radical having 1 to 4 carbon atoms; and R 5  represents an alkyl or cycloalkyl radical having 1 to 12 carbon atoms, a phenyl radical or a radical of the formula --C m  H 2m  --φ or C m  H 2m+1  --φ--, m being 1 to about 12. 
     The second class of complexing agents consists of cyclic polyethers having 6 to 30 atoms in the ring, preferably macrocyclic polyethers having 15 to 30 atoms in the ring, and built up from 2 to 10, preferably 4 to 10, --0--X units, in which X is either --CHR 6  --CHR 7  -- or --CHR 6  --CHR 8  --CR 9  R 7  --, where R 6 , R 7 , R 8  and R 9 , which are identical or different, are a hydrogen atom or an alkyl radical having 1 to 4 carbon atoms, and one of the X can be --CHR 6  --CHR 8  CR 9  R 7  -- if the --O--X units contain the grouping --O--CHR 6  --CHR 7  --. 
     The third class of complexing agents consists of the compounds of formulas IIa, IIb and IIc: ##STR2## wherein Z represents O or Y--R 10 , Y represents N or P, A represents an alkylene group having 1 to 3 carbon atoms, D represents O, S or N--R 11  where R 11  as an alkyl radical having 1 to 6 carbon atoms, R 10  represents an alkyl radical having 1 to 6 carbon atoms, and p, q and r, which are identical or different, are integers from 1 to 5. 
     In a preferred embodiment of the process of the invention, at least one sequestering agent of the formula (I) is used wherein R 1 , R 2 , R 3  and R 4  represent a hydrogen atom or a methyl radical, and R 5  and n have the meaning as described meaning. 
     The sequestering agents particularly preferred for use in the process are those wherein n is greater than or equal to 0 and smaller than or equal to 6, and wherein R 5  represents an alkyl radical having 1 to 4 carbon atoms. 
     Examples of sequestering agents suitable for use in the inventive process are: 
     tris-(3-oxabutyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.3)3 
    
     tris-(3-oxaheptyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 O--C.sub.4 H.sub.9 ).sub.3 
    
     tris-(3,6-dioxaheptyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.3).sub.3 
    
     tris-(3,6,9-trioxadecyl)-amine of the formula: 
     
         N--(CH.sub.2 CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.3).sub.3 
    
     tris-(3,6-dioxaoctyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--C.sub.2 H.sub.5).sub.3 
    
     tris-(3,6,9-trioxaundecyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--C.sub.2 H.sub.5).sub.3 
    
     tris-(3,6-dioxanonyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--C.sub.3 H.sub.7).sub.3 
    
     tris-(3,6,9-trioxadodecyl)-amine of the formula: 
     
         N--(CH.sub.2 CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--C.sub.3 H.sub.7).sub.3 
    
     tris-(3,6-dioxadecyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--C.sub.4 H.sub.9).sub.3 
    
     tris-(3,6,9-trioxatridecyl)-amine of the formula: 
     N--(CH 2  --CH 2  --O--CH 2  --CH 2  --O--CH 2  --CH 2  --O--C 4  H 9 ) 3   
     tris-(3,6,9,12-tetraoxatridecyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--(CH.sub.2 --CH.sub.2 --O--).sub.3 --CH.sub.3).sub.3 
    
     tris-(3,6-dioxa-4-methylheptyl)-amine of the formula: 
     
         N--(CH.sub.2 --CH.sub.2 --O--CHCH.sub.3 --CH.sub.2 --O--CH.sub.3).sub.3 
    
     tris-(3,6-dioxa-2,4-dimethylheptyl)-amine of the formula: 
     N--(CH 2  --CHCH 3  --O--CHCH 3  --CH 2  --O--CH 3 ) 3 . 
     The preferred compound of formula I is tris-(dioxaheptyl)amine. The preparation of these sequestering agents is described in French Patent Application No. 2,450,120. 
     Cyclic ethers useful in the process according to the invention comprise compounds such as dioxane or the macrocyclic ethers known generally &#34;crown ethers&#34;, which are described in French Patent No. 2,026,481. 
     The following are examples of crown ethers which can be used according to the invention: ##STR3## 
     Some of the compounds from the third class of complexing agents are described in French Patent No. 2,052,947. 
     The following are examples of compounds from this third class suitable for use in the process according to the invention: ##STR4## 
     According to a first preferred embodiment Of the invention, sodium tertiary-butylate is contacted with carbon dioxide, then trichloroacetyl chloride is added and subsequently, a supplementary quantity of tertiary-butylate is added. 
     The complexing agent is introduced at any time, during the carbonating or before the addition of the supplementary quantity of tertiary-butylate. 
     According to a second preferred embodiment, all the tertiary-butylate is introduced at the start of the reaction, and then the acid chloride is added, whereby the complexing agent is added at any time. 
     In yet another embodiment of the invention, all the tertiary-butylate is introduced o top of the acid chloride. 
     The reaction can be carried out in any solvent, whatever the nucleophilic character of the medium. The following solvents are useful in the inventive process. 
     aromatic hydrocarbon derivatives such as: benzene, the xylenes and toluene; 
     polar aprotic solvents such as: dimethylformamide, 
     oxygen-containing solvents such as: dioxane and diethylene and dimethylene glycols. 
     Generally, the best solvents have a melting point ≦10° C. and a boiling point ≦150° C., and are inert towards the reaction mixture and immiscible with water. 
     Moreover, it is advantageous if the partition coefficients of the complexing agent and the ditertiary-butyl dicarbonate between the organic phase and the aqueous phase are such that the complexing agent passes at least one hundred times more easily into the water than the ditertiary-butyl decarbonate. 
     Preferred solvents meeting the above limitations are aromatic solvents and petroleum fractions containing at least 50% of aromatics. 
     Preferably, the molar quantity of acid halide used is between 0.3 and 0.49 times the quantity of tertiary-butylate employed. The reaction temperature is advantageously between -10° C. and 60° C. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be described more completely by reference to the following examples which should not be considered as limiting the invention. 
     EXAMPLE 1 
     Standard operating procedure. Influence of the quantity of TDA 1   
     12.8 g of tBuONa (0.133 mole) and 75 ml of dry toluene were charged to a 250 ml reactor. 
     At ambient temperature, CO 2  was introduced which caused evolution of heat. The introduction was carried out for thirty minutes. The introduction of CO 2  was then stopped and the reaction mixture was cooled to 10° C., at which temperature x ml of TDA and then 9.7 g of trichloroacetyl chloride (0.0506 mole) dissolved in 30 ml of toluene, were added for the first time at 10° C. in 10 minutes. The reaction mixture was very thick. The temperature of the reaction mixture was then allowed to rise to ambient temperature and the mixture was then stirred for 5 hours and 30 minutes. 
     After cooling, 100 ml of ice water were added. After washing with 3×100 ml of water and drying over 15 g of sodium sulfate, the organic phase was evaporated at ambient temperature. 
     The orange-colored product obtained was analyzed by gas chromatography. 
     
         ______________________________________Experi-         Complexing  Temper-ment   Toluene  agent       ature  Duration                                     RY______________________________________Com-   75 + 30  --          25° C.                              5 h 30 6parison1      75 + 30  1 ml of TDA 1                       25° C.                              5 h 30 53           (0.003 mole)2      75 + 30  2 ml of TDA 1                       25° C.                              5 h 30 623      75 + 30  3 ml of TDA 1                       25° C.                              5 h 30 784      75 + 30  5 ml of TDA 1                       25° C.                              5 h 30 77.5______________________________________ RY is the yield relative to product introduced: ##STR5## 
    
     EXAMPLE 2 
     Influence of Temperature 
     The procedure of Example 1 was followed, charging 0.13 mole of sodium tertiary-butylate, 0.051 mole of trichloroacetyl chloride (TCAC), 75+30 ml of toluene and 5 ml of TDA 1 (0.0015 mole). 
     The carbonation was carried out at 10° C. and then, after running in the TCAC, the reaction temperature was taken to the value T given in the table. The duration of the reaction was 5 hours 30 minutes. 
     
         ______________________________________Experi-        Complexing  Temper-ment  Toluene  agent       ature  Duration                                    RY______________________________________5     75 + 30  5 ml of TDA 1                      10° C.                             5 h 30 79          (0.015 mole)6     75 + 30  5 ml of TDA 1                      20° C.                             5 h 30 77.57     75 + 30  5 ml of TDA 1                      28° C.                             5 h 30 768     75 + 30  5 ml of TDA 1                      50° C.                             5 h 30 77______________________________________ 
    
     EXAMPLE 3 
     Influence of the tBuONa/TCAC ratio 
     The procedure of Example 1 was followed, charging 0.13 mole of sodium tertiary-butylate (tBuONa), x moles of trichloroacetyl chloride (TCAC), 75+30 ml of toluene and 0.015 mole of TDA 1. The reaction was carried out for 5 hours and 30 minutes at 20°. 
     
         ______________________________________                    Excess of                    tBuONa over                    the stoi-Experi-         Moles of chiometric                             Temper-ment   Toluene  TCAC     amount   ature  RY______________________________________ 9     75 + 30  0.065    0        20° C.                                    52.510     75 + 30  0.062    4%       20° C.                                    79.511     75 + 30  0.059    9%       20° C.                                    80.512     75 + 30  0.051    21%      20° C.                                    77.5______________________________________ 
    
     EXAMPLE 4 
     Influence of the Duration 
     The procedure of Example 1 was followed, charging 0.13 mole of sodium tertiary-butylate, 0.51 mole of trichloroacetyl chloride, x+30 ml of toluene and 0.015 mole of TDA 1. The reaction was carried out for 5 hours 30 minutes at 20° C. 
     
         ______________________________________Experiment     Toluene      Temperature                             RY______________________________________13        35 + 30      20° C.                             3714        75 + 30      20° C.                             77.515        180 + 30     20° C.                             8216        290 + 30     20° C.                             77______________________________________ 
    
     EXAMPLE 5 
     Influence of Duration 
     The procedure of Example 1 was followed. In the comparative experiments, 0.13 mole of sodium tertiary-butylate, 10 ml of DMF (at the end of carbonation), 0.051 mole of trichloroacetyl chloride and 75+30 ml of toluene were charged. The reaction was carried out at 20° for a variable time. 
     
         ______________________________________                        Tem-             Complexing per-  Dura-Experiment    Toluene  solvent    ature tion  RY______________________________________Comparison    75 + 30  DMF 10 ml  10° C.                              1 h   9%with the pub-lication byPOZDEV,usingtoluene +DMFComparison    75 + 30  DMF 10 ml  20° C.                              3 h 30                                    42%with the pub-lication byPOZDEV,usingtoluene +DMFComparison    75 + 30  DMF 10 ml  20° C.                              5 h 30                                    51%with the pub-lication byPOZDEV,usingtoluene +DMFComparison    75 + 30  DMF 10 ml  20° C.                              16 h  57.3%with the pub-lication byPOZDEV,usingtoluene +DMF______________________________________ 
    
     The experiments were carried out with 0.13 mole of sodium tertiary-butylate, 0.051 mole of trichloroacetyl chloride, 75+30 ml of toluene and 0.015 mole of TDA 1 at a temperature of 20° C. 
     
         ______________________________________Experi-        Complexing  Temper-ment  Toluene  agent       ature  Duration                                    RY______________________________________17    75 + 30  5 ml of TDA 1                      20° C.                              1 h   7618    75 + 30  5 ml of TDA 1                      20° C.                              1 h 45                                    8219    75 + 30  5 ml of TDA 1                      20° C.                              5 h 30                                    77.520    75 + 30  5 ml of TDA 1                      20° C.                             22 h 30                                    75______________________________________ 
    
     EXAMPLE 6 
     Influence of the Solvent 
     The procedure of Example 1 was followed, charging 0.13 mole of tBuONa, 0.051 mole of TCAC when appropriate, 0.015 mole of TDA 1 and 75+30 ml of a solvent. 
     
         ______________________________________                        Tem-             Complexing per-  Dura-Experiment   Solvent   agent      ature tion  RY______________________________________Compar- Toluene              20° C.                              5 h 30                                    6%ison    (75 + 30) 4      Toluene   5 ml of    20° C.                              5 h 30                                    77.5%   (75 + 30) TDA 121      Dioxane              20° C.                              5 h 30                                    23   (75 + 30)22      Dioxane   5 ml of    20° C.                              5 h 30                                    69%   (75 + 30) TDA 123      Diglyme              20° C.                              5 h 30                                    40%   (75 + 30)______________________________________ 
    
     EXAMPLE 7 
     Influence of the Complexing Agent 
     The procedure of Example 1 was followed, with 0.13 mole of tBuONa, x moles of a complexing agent, 0.051 mole of TCAC and 75+30 ml of toluene. 
     
         ______________________________________Experi-         Complexing  Temper-ment   Toluene  agent       ature  Duration                                     RY______________________________________Compar-  75 + 30              20° C.                              5 h 30  6%ative24     75 + 30  Diglyme     20° C.                              5 h 30 43%           (0.13 mole)25     75 + 30  Dioxane     20° C.                              5 h 30 14%           (0.23 mole)______________________________________ 
    
     EXAMPLE 8 
     Influence of the Acid Halide 
     The procedure of Example 1 was followed, with 0.13 mole of tBuONa, 0.051 mole of acid chloride, 75+30 ml of toluene and 0.015 mole of TDA at a temperature of 20° C. for 5 hours 30 minutes. 
     
         ______________________________________Experi-        Acid       Temper-ment  Toluene  chloride   ature  Duration                                   RY______________________________________26    75 + 30  CCl.sub.3 COCl                     20° C.                            5 h 30 77.5%27    75 + 30  CHCL.sub.2 COCl                     20° C.                            5 h 30 5%28    75 + 30  CH.sub.2 ClCoCl                     20° C.                            5 h 30 5%______________________________________ 
    
     EXAMPLE 9 
     Change of Substrate 
     Ditertiary-amyl carbonate 
     8.1 g of sodium t-amylate (0.064 mole), 100 ml of toluene and 5 g of TDA 1 were introduced into a 250 ml reactor. CO 2  was injected into this suspension for 30 minutes, until the exit rate from the reactor was identical to the inlet rate. After cooling to 0° C., 3.8 g of dichloroacetyl chloride (0.0258 mole) were run within 10 minutes. The reaction mixture was then heated again to 20°, where it was stirred for five hours. After washing, the organic phase was dried and evaporated. 1.7 g of an aqueous product were recovered, in which NMR analysis gave 88% of ditertiary-amyl carbonate, corresponding to a relative yield of 23.5% based on dichloroacetyl chloride employed.
The present invention relates to a novel process for the preparation of a ditertiary-alkyl dicarbonate from an acid halide in the presence of a complexing agent. More particularly, it relates to the preparation of a ditertiary-butyl dicarbonate.