DE2139211C3 - Process for the isolation of trifluoroacetaldehyde from fluorination products of chlorai in the form of hemiacetals - Google Patents

Description

CF ₃ CH-OR
OH

converted, in which R is a straight-chain or branched alkyl radical with 1 -5 C atoms, then or simultaneously converts the hydrogen fluoride present with a Si compound to SiF *, by heating or passing through an inert gas SiF * and possibly HC! drives out and from the The crude product obtained in this way is the trifluoroacetaldehyde hemiacetal separated by fractional distillation.

25th

anhydrous form is available. This is with the known sensitivity of perhalogenated aldehydes as opposed to alkalis, the removal of acids by neutralization with bases cannot be done without complete avoidance the so-called haloform reaction possible.

According to DAS 12 87 056, the adduct CF3CHOHF can be broken up with the aid of NaF and the hydrogen fluoride released can be bound to NaF by chemisorption. The prerequisite for using this process on fluorination mixtures CF ₃ CHO-HF / HF / HC1 is - as described - the most complete possible separation of the hydrogen chloride by distillation, since it cannot be removed by means of NaF. In addition, its presence has a disruptive effect on the HF adsorption by NaF and promotes the polymerization of the free trifluoroacetaldehyde at the required temperatures of 50-100 ° C. Furthermore, the process is difficult to control so that hydrogen fluoride is completely separated off, since NaF HF is predominantly chemisorbed at some temperatures and desorbed at others

There has now been a process for the isolation of trifluoroacetaldehyde in the form of a hemiacetal from Found trifluoroacetaldehyde, hydrogen fluoride and optionally mixtures containing hydrogen chloride, which is characterized in that the trifluoroacetaldehyde contained in the mixtures in one Hemiacetal of the formula

CF ₁ CH-OR
OH

It is known to produce trifluoroacetaldehyde from chloral by fluorination with hydrogen fluoride in a continuous, catalyzed vapor phase process (DBP 14 43 837). For complete conversion of CCIjCHO into CF ₃ CHO while largely avoiding the intermediate stages CFCI ₂ CHO and CF ₂ CICHO, the use of an excess, e.g. B. of 4 moles of HF per mole of CChCHO, has been found to be necessary. The natural consequence of this is that the trifluoroacetaldehyde in the crude fluorination product is mixed not only with hydrogen chloride but also with the excess hydrogen fluoride. With these mineral acids it forms 1:! Adducts, of which the CF ₃ CHOHF can even be distilled (boiling point + 38 "C).

The problem therefore arises, from mixtures of this type, to obtain the trifluoroacetaldehyde acid-free and in in a form that ensures that it can be easily reused.

For the cleavage of the adducts and the separation of the acids from trifluoroacetaldehyde, water is little suitable because it forms a very stable hydrate with the perfluorinated aldehyde, which is difficult to convert into acidic and 35

converted, in which R is a straight-chain or branched alkyl radical with 1-5 C atoms, thereafter or simultaneously converts the hydrogen fluoride present with a Si compound to SiF *, through Heating or passing through an inert gas drives out SiF * and optionally HCl and from the so obtained The crude product, the trifluoroacetaldehyde hemiacetal, is separated off by fractional distillation.

The method according to the invention can be carried out in different

various variations can be carried out. Advantageously, the mixture containing the trifluoroacetaldehyde contains ("fluorination product") an orthosilicic acid ester of the formula Si (OR) *, where R is the above Has meaning. The hemiacetal is formed and SiF * escapes. The silicic acid ester is in such Quantities - or a small excess, up to 10% - added that the two compounds trifluoroacetaldehyde or hydrogen fluoride, which are present in the mixture, are completely converted.

The conversion of the mixtures containing the aldehyde takes place in this case according to the equation

CF., CHO • HF + "HF +" iHCI +

/ 1 + I
4th

Si (OR) ₄ > CF., fH (OH) OR + «ROH +

/ 1 + I

SiF ₄ -f mHCI

Here, η and m denote the content of HF or HCl (in mol) per mole of CF ₃ CHO-HF present in the starting mixture.

But you can also add an alcohol ROH to the mixture containing the trifluoroacetaldehyde (where R has the meaning given above), convert the aldehyde to the hemiacetal and then convert the hydrogen fluoride to SiF * (e.g. using SiCl *) .
You can also condense the gaseous fluorination mixture or an equivalent mixture directly in an alcohol, with most of the hydrogen chloride formed in the fluorination in the

Gas phase remains and can be worked up separately, and then one to this mixture Add silicon compound such as SiCU. This reaction proceeds according to the following reaction scheme;

! 'SiCI ₊ - CF ₃ CH (OH) OR +

SiF ₄ + (m + / j + I) HCI

In the last two cases, it is advisable to use the alcohol in an amount equivalent to the trifluoroacetaldehyde present and the silicon compound, in particular SiCU, in an amount equivalent to the amount of hydrogen fluoride present, advantageously both components in a slight excess - up to tO%, preferably up to 3% - admitted. The reaction temperatures when working under normal pressure, which is preferred, at -2O ⁰ C to +30 ⁰ C, preferably -10 to +20 ⁰ C. A working under pressure and higher temperatures is possible in itself, but it does not bring any special Vorteite ; the same is true of the use of a mistletoe. The reaction time is not critical; it should be chosen so that the heat of reaction is dissipated and the desired reaction temperature is maintained. The release of the SiF ₄ and, if applicable, the HCl generally takes place to the extent that the Si compound is added. In order to achieve complete removal of the acidic component, either an inert gas (nitrogen, air) is blown through or the crude product is refluxed after the addition has ended

The hemiacetals of triflioacetaldehyde obtained by the process according to the invention are after the commentary analysis and, after evaluating the NMk spectra, 93 to 97% of Ci jCH (OH) OR; she become contaminated by the alcohols from which they are made. You put lay. .-able forms of the Ti ifluoroacetaldehyds that from them after known methods can be obtained; because of their known similar reaction behavior, they can also be used instead of trifluoroacetaldehyde in some of its reactions are used and are important as valuable intermediates.

The process according to the invention uses the form of hemiacetal for the first time to isolate trifluoroacetaldehyde from the mixtures with HCl and HF in fluorination products of chloral with HF and to remove the HF present as SiF ₄ by reaction with silicon tetrachloride.

It is superior to the known processes in that the fluorination products can be reacted without pretreatment, in particular without removing hydrogen chloride, that trifluoroacetaldehyde cannot be lost through conversion into the hemiacetals either through decomposition or through polymerization and that the CF ₃ CHO, which is gaseous per se immediately in the form of the hemiacetals, which are stable and easily transportable at room temperature, which are liquid at room temperature and from which it can be obtained as such by reaction with H2SO4 or polyphosphoric acid by known processes.

What is surprising about the process according to the invention is that the _{hemiacetals obtained by reacting the adduct CF 1} CHO-HF with the alcohols mentioned, from which the hydrogen fluoride cannot be expelled by refluxing or by purging nitrogen, results in the hydrogen fluoride in the form of Silicium tetrafluoride and the hydrogen chloride can be eliminated practically quantitatively by precisely these measures, so that trifluoroacetaldehyde can be isolated from fluorination mixtures in the form of hemiacetals without great effort.

example 1
Trifluoroacetaldehyde ethyl hemiacetal

in a t-liter plastic vessel with a thermometer sleeve and two tubes for a copper cooler cooled with ice water and a dropping funnel become 360 g submitted a fluorination product of chloral, in which by titration the content of HF to 4.2 mol and which has been determined to be 1.12 mol of HCI Hours 220 g (1.06 mol) of ethyl orthosilicate Si (OC2H5) i were added dropwise. The immediately occurring violent one

2) reaction by external cooling of - throttled 10 ⁰ C, but the internal temperature is 20 ⁰ C or at + and acid gases (HCl, SiF develop _4). Shortly before the end of the plugging of Si (OQHs) _{4, the} evolution of heat and gas cease. After 4 hours

Boiling under reflux, further acidic gases being driven out, the residue is fractionally distilled. With a boiling point of 103-104.5 ° C./749 mm, 261 g of CF ₃ CH (OH) OC ₂ H _{5 are} isolated (76% yield, based on the organic product initially charged).

CFjCH (OHPC ₂ H ₅ (MW = 144)

Calculated: C 33.4, H 4.9, F 39.6;
Found: C 343. H 5.4. F 35.6.

_{4 ()} Purity estimated from the NMR spectrum, 93.5%.
Calculated for this:

C 34.6, H 5.4, H 5.4, F 36.9.

Example 2
Trifluoroacetaldehyde methyl hemiacetal

245 g of a fluorination product of chloral, the 1.705 mol CFjCHO, 2.52 mol HF and 0.76 mol HCI are in a 1 liter plastic jar with

-><> Copper cooler, thermometer and dropping funnel (as in Example I) first within 15 minutes with 55 g (1.72 mol) CH ₃ OH, then with vigorous stirring with a magnetic stirrer and external cooling drop by drop within one hour with 103 g ( 0.635 moles) SiCl ₄

v, offset. In the process, HCl and SiF ₄ develop, which are virtually quantitatively removed from the product by refluxing. The subsequent distillation in a packed silver jacket column gives 203 g of CFj-CH (OH) OCHj

M> boiling point 96-97 ° C / 749 mm (yield: 92%).

CF) CH (OH) OCH] (MW = 130)
Calc .: C2 / .7, H 3.9, F 43.9;
Found: C 27.6, H 4.0, F 42.5.

^"R> From NMR spectrum estimated purity 97%.
Calculated for this:

C 28.1, H 4.1. F 42.5.

Example 3 Trifluoroacetaldebyd isopropyl hemiacetal

Within 5.5 hours, 476 g of gaseous product of the fluorination of chloral with HF - as described in DBP 14 43 837 - are absorbed in 180 g (3 mol) of isopropyl alcohol, which is in a plastic vessel cooled to 0 ° C with attached, also at 0 ⁰ C held cooler. The absorbed substance consists of 45 g (1.26 mol) HCl, 162 g (8.1 mol) HF and 269 g (2.75 mol) CF ₃ CHO. By adding dropwise 345 g (2.03 mol) of SiCl ₄ within 1.5

10 hours, expel the acidic gases (HCI, SiF ₄ ) by introducing nitrogen and subsequent fractional distillation, 369 g of CF ₃ CH (OH) OCH- (CH ₃ ) J are obtained with a boiling point of 102-104.5 ° C / 754 mm ( Yield 83%).

CF ₃ CH (OH) OCH (Ch ₃ ) J (MW = 156) Calculated: C 38.0, H 5.7, F 36.1, found: C 38.0, H 5.9, F 33 , 9.

Example 4 Trifluoroacetaldehyde n-amyl hemiacetal

Analogously to Example 2, 234.5 g of a fluorination product of chloral containing 1.595 mol CF ₃ CHO, 238 mol HF and 0.74 mol HCl are added within 40 minutes with 141 g (1.6 mol) of η-amyl alcohol at a temperature of 20 ⁰ C offset. Then are added dropwise within 45 minutes at a bath temperature of +10 ⁰ C HOG (0.65 M'ol) SiCl in the mixture, with acidic gases _(SiF4, HCI). The reaction mixture (5 hours) heated to evolution of gas to 80-90 ⁰ C, then gassed a further 8 hours at room temperature with nitrogen.

In the subsequent fractional distillation, 206 g

CF ₃ CH (OH) OCH ₂ CH ₂ CH ₂ Ch ₂ CH ₃

obtained with a boiling point of 60-61 ° C / 10 mm (Yield: 69.5%).

CF ₃ CH (OH) OCH ₂ CH ₂ CH ₂ CH ₂ Ch ₃ (MW: 186)

Calc .: C 45.2, H 7.0 F 30.6; Found: C 48.4, H 8.1, F 25.7.

Purity estimated from the NMR spectrum 85%. Calculated for this:

C 48.6, H 8.0, F 25.9.

Claims (1)

Claim: Process for the isolation of trifluoroacetaldehyde in the form of a hemiacetal from trifluoroacetaldehyde, Hydrogen fluoride and optionally mixtures containing hydrogen chloride, characterized in that that the trifluoroacetaldehyde is converted into a hemiacetal of the general formula