GB2561538A

GB2561538A - Improved drying agent for electronic circuits

Info

Publication number: GB2561538A
Application number: GB1703665.8A
Authority: GB
Inventors: Wilhelm Wieland Friedrich
Original assignee: WIELAND KG
Current assignee: WIELAND KG
Priority date: 2017-03-07
Filing date: 2017-03-07
Publication date: 2018-10-24
Anticipated expiration: 2037-03-07
Also published as: GB201703665D0; GB2561538B

Abstract

A liquid drying composition for drying of electrical, electronic and optical systems, as well as drying material samples, comprising: an alkylorthocarboxylic ester R1-C(OR2)3 or an alkylorthocarbonate; and a volatile and non-corrosive catalyst or precursor for a catalyst for hydrolysis of said alkylorthocarboxylic ester or alkylorthocarbonate. The alkylorthocarboxylic ester can be triethyl orthoformate, trimethyl orthoformate, trimethyl orthoacetate or triethyl orthoacetate. The composition may also comprise a volatile Lewis acid, a volatile sulfonic acid, a volatile carboxylic acid or readily hydrolyzable esters of the volatile sulfonic acids or readily hydrolyzable esters of volatile carboxylic acids as the catalyst or catalyst precursor. The catalyst precursor may be a perfluoroalkylcarboxylate, alkyl trifluoroacetate, ethyl trifluoroacetate, methyl trifluroeacetate, alkyl trifluoromethansulfonate, ethyl trifluoromethansulfonate or methyl trifluoromethansulfonate. The composition can further comprise a solvent such as isopropanol, ethanol, tetrahydrofuran or 1,4-dioxane. Also disclosed is a process for drying electrical, electronic or optical devices by bringing into contact said device with the liquid composition. The catalyst precursor reacts with water to form a catalyst for hydrolysis of the ortho ester. The catalyst formed may be volatile and may have a boiling point of less than 75 °C.

Description

(71) Applicant(s):

Friedrich Wilhelm Wieland

Koelner Str. 38B, Luedenscheid 58509, NW, Germany

Wieland KG

Koelner Str. 38 B, Luedenscheid 58509, D, Germany (51) INT CL:

B01D 12/00 (2006.01) (56) Documents Cited:

WO 2014/174290 A1 WO 2010/122150 A1 DD 000278336 A1 DE 102016217050 A1

US 4390417 A (58) Field of Search:

INT CL B01D, C02F, F26B

Other: EPODOC, WPI, XPESP, Springer and Patent Fulltext (72) Inventor(s):

Friedrich Wilhelm Wieland (74) Agent and/or Address for Service:

Friedrich Wilhelm Wieland

Koelner Str. 38B, Luedenscheid 58509, NW, Germany (54) Title of the Invention: Improved drying agent for electronic circuits

Abstract Title: Liquid desiccant preparation for drying electrical, electronic and optical systems, comprises orthoalkylcarboxylic acid alkyl ester or alkyl orthocarbonate (57) A liquid drying composition for drying of electrical, electronic and optical systems, as well as drying material samples, comprising: an alkylorthocarboxylic ester R₁-C(OR₂)₃ or an alkylorthocarbonate; and a volatile and noncorrosive catalyst or precursor for a catalyst for hydrolysis of said alkylorthocarboxylic ester or alkylorthocarbonate. The alkylorthocarboxylic ester can be triethyl orthoformate, trimethyl orthoformate, trimethyl orthoacetate or triethyl orthoacetate. The composition may also comprise a volatile Lewis acid, a volatile sulfonic acid, a volatile carboxylic acid or readily hydrolyzable esters of the volatile sulfonic acids or readily hydrolyzable esters of volatile carboxylic acids as the catalyst or catalyst precursor. The catalyst precursor may be a perfluoroalkylcarboxylate, alkyl trifluoroacetate, ethyl trifluoroacetate, methyl trifluroeacetate, alkyl trifluoromethansulfonate, ethyl trifluoromethansulfonate or methyl trifluoromethansulfonate. The composition can further comprise a solvent such as isopropanol, ethanol, tetrahydrofuran or 1,4-dioxane. Also disclosed is a process for drying electrical, electronic or optical devices by bringing into contact said device with the liquid composition. The catalyst precursor reacts with water to form a catalyst for hydrolysis of the ortho ester. The catalyst formed may be volatile and may have a boiling point of less than 75 °C.

Tide: Improved Drying Agent for Electronic Circuits by

Friedrich W. Wieland

FIELD OF THE INVENTION [0001] This invention relates to drying agents. More specifically this invention relates to drying agents for electronic circuits that are used as a spray.

BACKGROUND [0002] Electronic devices and electronic circuits are frequently damaged by moisture and water. Even quite small leak currents can interrupt the operation of high-impedance circuits (such as CMOS-circuits) or high-voltage circuits such as the ignition system of cars up to a complete malfunction. Prior art “water displacing spray” or “penetrating oil” only move water on printed circuit boards (PCB) or in a casing by coating the printed circuit board (or metal parts) with a thin layer of non-conducting oil and mechanically flush away some water. In this way they sometimes restore function of electronics of little sensitivity. However the water in the circuit isn't completely removed so a reproducable repair of such circuits isn't ensured.

[0003] For the foregoing reasons, there is a need for an improved drying agent that removes water and can be applied easily like a conventional water displacing spray.

SUMMARY [0004] The present invention is directed to a drying agent that solves these problems.

[0005] It was found that water and moisture dissolves some residues of solder flux and that ion-conducting solutions are produced on a printed circuit board (PCB). These solutions are the reason for the considerable leak currents produced by water in an electronic device.

It was found that in order to remove this conductivity it is necessary to remove the water completely from the solution by a chemical reaction.

[0006] The same problem arises during drying of precision optics such as binoculars or drying of biological samples which can be also solved in this way.

[0007] It was discovered that a solution comprising orthoesters such as trimethyl orthoformate or triethyl othoformate and a volatile, non-corrosive catalyst can even remove small traces of water within a very short time and can effectively restore the functionality of circuits that are damaged by water and moisture even for sensitive circuit with a high impedance.

[0008] Within this patent application a catalyst is called „volatile“ that has a boiling point of less than 100°C. A catalyst with a boiling point of less than 75°C is called „very volatile.

[0009] As catalysts preferred are volatile, neutral esters of perfluoroacetic acid that were discovered as catalysts for the hydrolysis of orthoesters. In this way sensitive electronics are not damaged by the dry product and the removal of drying agent e.g. by evaporation is complete within a rather short period of time. On the other hand said drying compositions remove nearly all watersoluble and reduce the conductivity of the resulting mixture of drying agent, water and flux residues such as abietic acid or of dicarboxylic acids within seconds to very low values preventing electrocorrosion.

[0010] These and the other features, aspects and advantages of the present invention are better understood with respect to the following description and appended claims.

DETAILED DESCRIPTION [0011] Electronic circuits and devices are frequently damaged by water and moisture. For example cell phones are frequendy dropped into water or damaged by rainwater. Computer keyboards are frequently damaged by beverages. Even rather small leakage currents produced by water and aqueous solutions of flux residues can seriously affect the operation of electronics up to a complete failure of high impedance (e.g MOS) circuits due to the high impedance of MOS-circuits.

State of the art “water displacing sprays” only move water on the printed circuit board (PCB) or within the chassis by covering the printed circuit board with a thin layer of mineral oil and by purely mechanical action. In this way the functionality of some circuits might be restored but the water within the electronic device is not completely removed. Because of this reason a failure might occur later during operation. Such a failure of e.g. an ignition system of a car on a highway, autobahn etc. might produce a very dangerous situation up to an accident.

[0012] Other methods to dry electronics such as the use of a large amount of anhydrous alcohols such as absolute ethanol or isopropyl alcohol have the disadvantage that the water is removed with large amounts of expensive anhydrous alcohols in order to dilute it and wash the water away. By this method large amounts of mixtures of organic solvents and water are produced that must be disposed as hazardous waste.

[0013] It was found that sprays comprising orthoesters of carboxylic acids such as orthoesters of formic acid such as triethyl orthoformate or trimethyl orthoformate in presence of suitable catalysts can remove even small traces of water nearly completely from electronic devices and recover operability of even sensitive high impedance electronics and prevent damage to the electronic devices.

[0014] Suitable orthoesters for compositions according to the present invention are orthoesters of alkylcarboxylic acids and arylcarboxylic acids although orthoesters of carbonic acids might be usable, too. Preferred orthoesters for compositions according to the present invention are orthoesters of formic acid, acetic acid and propionic acid, in particular orthoesters with Ci-C4_alcohols (methanol to butanol) such as their methyl- or ethylesters. Most preferred are orthoesters of formic acid with Ci-C4_alcohols (methanol to butanol) and orthoesters of acetic acid (triethyl orthoacetate und trimethyl orthoacetate). Trimethyl orthoformate und triethyl orthoformate and triethyl orthoacetate are optimum.

[0015] The above compositions according to the present invention may be further comprising solvents that are indifferent to PCBs and electronic components, especially isopropyl alcohol or ethanol.

[0016] Preferred solvents are non-conducting aprotic solvents that are miscible with water such as tetrahydrofurane or 1,4-dioxane although other less polar solvents might be suitable, too.

[0017] Also more preferred are perfluorinated non-combustible organic solvents with polar groups such as perfluorotetrahydrofurane although less polar perfluorinated solvents might be usable, too. [0018] Suitable catalysts are Lewis-acids such as BF₃. Bronsted-acids such as sulfonic acids, polymeric cation exchange resins in sulfonic acid-form particularly as powder or nanopowder such as the polymer commercially obtainable under the trademark „NAFION“(RTM) from E.I. DuPont de Nemours und Company, Wilmington, Delaware, USA and methanesulfonic acid. Carboxylic acids such as acetic acids are less preferred.

[0019] Volatile acids in the sense of this patent application are all acids that have a boiling point of 72.5°C (boiling point of trifluoroacetic acid) or less. The term „ester of trifluoroacetic acid“ in patent claims of this patent application also comprises esters of other halogenated derivatives of acetic acid such as chloroacetic acid. Other esters of carboxylic acids with a substituent with a -I inductive effect such as halogens, the nitro-group and the cyano-group might be usable, too, although the esters of nitroacetic acid, cyanoacetic acid, pyruvic acid or glycolic acid and glycine are less volatile and therefore less preferred.

[0020] Preferred catalysts are volatile acids that do not attack the substrate that shall be dried (e.g. a printed circuit board or an integrated circuit).

[0021] Also preferred catalysts are volatile Lewis-acids that are indifferent to the substrate such as boron trifluoride (e.g. dissolved in ether) although gases with Lewis acid properties such as sulfur dioxide may be suitable, too. However those acids might cause corrosion of metal parts of electronic devices and electronic components. Moreover some of those acids hydrolyze in water to toxic hydrofluoric acid.

[0022] More preferred catalysts according to an embodiment of the present invention are volatile fluorinated carboxylic acids such as trifluoroacetic acid and the anhydride of trifluoroacetic acid. However these acids are corrosive as the above Lewis- and Bronsted-acids and dissolve metals of spray cans during production and storage. Moreover they react with orthoesters during storage. [0023] Most preferred according to a further embodiment of the present invention are easily hydrolyzable esters of fluorinated volatile carboxylic acids such as trifluoroacetic acid, in particular esters of the same alcohol that is bound in the orthoester that hydrolyze readily into free trifluoroacetic acid in contact to water without the use of further catalysts for this hydrolysis although a different lower alcohol may be used, too. The trifluoroacetic acid formed by hydrolysis acts as an effective temporary catalyst for the hydrolysis of the orthoester. The trifluoroacetic acid may at least partially react with an excess of orthoester to the neutral ester of trifluoroacetic acid that readily evaporates as easily the free acid after use so no residue is formed on the substrate such as a printed circuit board (PCB). A composition comprising trimethyl orthofomate or triethyl orthoformate further comprising ethyl trifluoroacetate or methyl trifluoroacetate as volatile catalyst is most preferred. A composition comprising trimethyl orthofomate and ethyl trifluoroacetate or methyl trifluoroacetate is optimum and allows rapid and complete drying. Within this patent application these esters are also called precursors for catalysts for hydrolysis of the above orthoesters.

[0024] According to a further embodiment of the present invention sulfonic acids such as perfluoralkyl sulfonic acids such as trifluoromethan sulfonic acid (also known as „triflic acid“) are also preferred. More preferred are esters of such fluorinated sulfonic acids such as methyl triflate or other lower alkyl triflates such as ethyl triflate that readily hydrolyze into sulfonic acid by water that can be converted back to the volatile ester by the reaction with an excess of orthoester.

Because of the high reactivity of the triflates and their alkylating properties and the higher boiling point of the corresponding free sulfonic acids this embodiment of the present invention is less preferred than the previous embodiment using esters of trifluoroacetic acid.

[0025] Also preferred are esters of methane sulfonic acid (mesylates). Less preferred are esters of non-volatile sulfonic acids such as tosylates or brosylates because they form residues on the substrate that has to be dried.

[0026] Catalyst concentrations of about 2 % (by weight) and 50 % (by weight based on sum of the mass of the orthoester and the mass of the ester of a trifluoroalkylcarboxylic acid or trifluoroalkylsulfonic acid) are preferred. Catalyst concentrations of about 2 % (by weight) and 50 % (by weight) are more preferred. A concentration between about

Am starksten bevorzugt ist ftir empfindliche Gerate eine Konzentration zwischen 4 Gew.-% und 10 Gew.-%.

[0027] Drying agents according to the present invention remove up to 95% of water within seconds and reduce the conductivity of aqueous solutions on printed circuit boards from values of up to 386 pS/cm (for a saturated solution of 115 mg adipic acid in 16.86 g water as simulated aqueous solution of flux residue) to values of 2 pS/cm or less. In such a way the electrocorrosion that would be unevitable without removal of water is suppressed effectively.

[0028] At the same time drying agents according to the present invention in contact with deionized water do not show an increased conductivity in water because the composition comprise no strong acids as catalysts. The measurement for the conductivity of the reaction products of a sample of 103.5 mg water with 7.24 g drying agent composition according to the present invention according to example 1 yielded a conductivity of «1 pS/cm.

[0029] Drying agent compositions according to the present invention may be further comprising a propellant gas such as carbon dioxide. The drying agents may be further comprising a moisture indicator such as a cobalt compound or an organic moisture indicator.

[0030] The following examples illustrate the best mode of carrying out the embodiments of the invention. Examples 1 to 3 illustrate the manufacture and use of drying agents according to the present invention.

EXAMPLES

Example 1

Manufacture of a drying agent composition [0031] 7.78 g Trimethyl orthoformate (99.8% dry, Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) are mixed in glass beaker with mit 0.33 g ethyl trifluoroacetate (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) by 10-minutes of stirring using a magnetic stirrer at room temperature. The composition is stored in a borosilicate glass bottle with a cap with a PTFE-gasket.

Example 2

Drying of a wet glass beaker [0032] 96.1 mg water (ion chromatography quality) are filled into a 100 ml Duran glass beaker.

Subsequently 0.8668 g of the drying agent composition from Example 1 are added. The sample is stored in the covered beaker at room temperature for 10 minutes.

Example 3

Determination of water residues by Karl-Fischer-Titration [0033] 17.1 g dry methanol (commonly sold under the trademark „HYDRANAL“(RTM) by Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) are placed in a 250 ml Duran glass beaker, and are dried with Karl-Fischer-solution (commonly sold under the trademark „HYDRANALComposite 5“(RTM) by Sigma-Aldrich Chemie GmbH, Taufkirchen) and the sample from Example 2 are added and titrated using Karl-Fischer-solution „HYDRANAL-Composite 5“(RTM). A remaining water content of 7 mg water was determined. Therefore, 93% of the added water are removed at room temperature within a few minutes. The remaining glass beaker from Example 2 is dry and clean after evaporation of traces of drying agent.

Example 4

Removal of water within 20 Minutes [0034] A sample of 109.1 mg water (Ion chromatography-Quality) is mixed with a solution of 0.2772 g ethyl trifluoroacetate (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) in 5.40 g Trimethyl orthoformiate (Sigma-Aldrich Chemie, Taufkirchen) and stirred for 15 minutes at room temperature using a magnetic stirrer. After 20 minutes the wasser content of the sample is determined by Karl-Fischer-Titration (in 12.71 ml dry methanol, HYDRANAL(RTM)). The above sample had a content of only 6 mg water, i.e. 94.5% of the water was immediately chemically removed from the solution.

Example 5

Removal of water by a Trimethylorthoacetate composition [0035] 127.9 mg ethyltrifluoroacetate (Sigma-Aldrich Chemie GmbH, Taufkirchen) are dissolved in 2.8427 g of trimethylorthoacetate (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) in a Duran glass beaker. The solution is added to 115.7 mg Wasser at room temperature. Immediately in is visible that the aqueous phase disappears. By Karl-Fischer-Titration a water content of 13 mg was determined.

Example 6

Preparation of a simulated aqueous extract of a no-clean-flux [0036] 19.5 mg adipic acid (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany) are dissolved in 18.06 g water (ionen chromatography-Quality). The solution has properties of water that wetted solder joints with residue from soldering with flux comprising adipic acid on a printed circuit board and has a specific conductivity of 226 pS/cm (measured using a conductivity tester „DIST 3“ manufactured by Fa. Hanna Instruments Inc., Woonsocket, Rhode Island, USA).

Example 7

Reduction of the specific conductivity by the drying agent [0037] 0 .5278 g of the adipic acid solution from Example 6 are mixed with a drying composition of 0.2772g Ethyltrifluoroacetate (Sigma-Aldrich Chemie GmbH, Taufkirchen) in 5.40 g Trimethylorthoformiate (Sigma-Aldrich Chemie GmbH, Taufkirchen) at room temperature. After about 2 minutes the conductivity is determined. A value of 2 bis 3 pS/cm is measured. The result shows how the drying agent reduces conductivity and therefore prevents electrocorrosion.

[0038] The present invention is commercially applicable for drying of wet electronic circuits.

[0039] Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other versions are possible. For example it is possible to use a mixture of catalysts. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.

[0040] The reader's attention is directed to all papers and documents which are filed concurrently with this specification, and the contents of all such papers and documents are incorporated herein by reference. All the features disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function, is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. § 112, 5| 6. In particular the use of “step of” in the claims herein is not intended to invoke the provisions of 35 U.S.C. § 112, 5| 6.

[0041] Insofar the description above and the accompanying drawings disclose any additional subject matter that is not within the scope of the claims below, the inventions are not dedicated to the public and the right to file one or more applications to claim such additional inventions is reserved.

Claims

CLAIMS: What is claimed is:

1. Liquid drying composition for drying of electrical, electronic and optical systems as well as for drying of material samples, comprising:

(a) an alkylorthocarboxylic ester Ri-C(OR.2)3 or an alkylorthocarbonate;

(b) a volatile and non-corrosive catalyst or precursor for a catalyst for hydrolysis of said alkylorthocarboxylic ester or alkylorthocarbonate.

2. Liquid drying composition according to claim 1, wherein said precursor for a catalyst reacts with water to form a catalyst for hydrolysis of said ortho esters.

3. Liquid drying composition according to claim 1 or claim 2, wherein said precursor forms a catalyst by hydrolysis that is volatile.

4. Liquid drying composition according to any one of claims 1 to claim 3, wherein said precursor forms a catalyst by hydrolysis that has a boiling point of less than 75°C.

5. Liquid drying composition according to any one of claims 1 to claim 4, wherein said volatile precursor for a catalyst is formed back from said catalyst by reaction with said ortho esters.

6. Liquid drying composition according to any one of claims 1 to claim 5, wherein said alkylortho carboxylic ester is selected from the group consisting of triethyl orthoformiate, trimethyl orthoformiate, trimethyl orthoacetate, and triethyl orthoacetate.

7. Liquid drying composition according to any one of claims 1 to claim 6, comprising at least one volatile Lewis-acid, at least one volatile sulfonic acid, at least one volatile carboxylic acid or at least one easily hydrolyzable ester of volatile sulfonic acids or at least one easily hydrolyzable ester of volatile carboxylic acids as catalyst or catalyst precursor.

8. Liquid drying composition according to any one of claims 1 to claim 7, comprising at least one perfluoroalkylcarboxylate CnF2n+iCOOR as catalyst precursor.

9. Liquid drying composition according to any one of claims 1 to claim 8, comprising at least one alkyl trifluoroacetate as catalyst precursor.

10. Liquid drying composition according to any one of claims 1 to claim 9, comprising ethyl trifluoroacetate or methyl trifluoroacetate as catalyst precursor.

11. Liquid drying composition according to any one of claims 1 to claim 7, comprising at least one alkyl trifluoromethansulfonate as catalyst precursor.

12. Liquid drying composition according to any one of claims 1 to claim 7 or claimll, comprising ethyl trifluoromethansulfonate or methyl trifluoromethansulfonate.

13. Liquid drying composition according to any one of claims 1 to claim 12, further comprising at least one solvent selected from the group consisting of isopropanol, ethanol, tetrahydrofuran or 1,4-dioxan.

14. Liquid drying composition according to any one of claims 1 to claim 13, comprising trimethyl orthoformiate as ortho ester and ethyl trifluoroacetate as catalyst precursor.

15. Liquid drying composition according to any one of claims 1 to claim 14, comprising trimethyl orthoformiate as ortho ester and at least 4 weight-% ethyl trifluoroacetate as catalyst precursor.

16. Process for drying electrical, electronic or optical devices comprising the step of:

-bringing in contact said electrical, electronic or optical devices with a liquid drying composition comprising:

(a) an alkylorthocarboxylic ester Ri-C(OR2)3 or an alkylorthocarbonate;

17. Process according to claim 16, wherein said precursor for a catalyst reacts with water to form a catalyst for hydrolysis of said ortho esters.

18. Process according to claim 16 or claim 17, wherein said precursor forms a catalyst by hydrolysis that is volatile.

19. Process according to any of claims 16 to claim 18, wherein said precursor forms a catalyst by hydrolysis that has a boiling point of less than 75°C..

20. Process according to any of claims 16 to claim 19, wherein said volatile precursor for a catalyst is formed back from said catalyst by reaction with said ortho esters.

21. Process according to any of claims 16 to claim 20, wherein said alkylortho carboxylic ester is selected from the group consisting of triethyl orthoformiate, trimethyl orthoformiate, trimethyl orthoacetate, and triethyl orthoacetate.

22. Process according to any of claims 16 to claim 21, wherein said drying composition is comprising at least one volatile Lewis-acid, at least one volatile sulfonic acid, at least one volatile carboxylic acid or at least one easily hydrolyzable ester of volatile sulfonic acids or at least one easily hydrolyzable ester of volatile carboxylic acids as catalyst or catalyst precursor.

23. Process according to any of claims 16 to claim 22, wherein said drying composition is comprising at least one perfluoroalkylcarboxylate CnF2n+iCOOR as catalyst precursor.

24. Process according to any of claims 16 to claim 23, wherein said drying composition is comprising at least one alkyl trifluoroacetate as catalyst precursor.

25. Process according to any of claims 16 to claim 24, wherein said drying composition is comprising ethyl trifluoroacetate or methyl trifluoroacetate as catalyst precursor.

26. Process according to any of claims 16 to claim 22, wherein said drying composition is comprising at least one alkyl trifluoromethansulfonate as catalyst precursor.

27. Process according to any of claims 16 to claim 22 or claim 26, wherein said drying composition is comprising ethyl trifluoromethansulfonate or methyl trifluoromethansulfonate.

28. Process according to any of claims 16 to claim 27, wherein said drying composition is further comprising at least one solvent selected from the group consisting of isopropanol, ethanol, tetrahydrofuran or 1,4-dioxan.

29. Process according to any of claims 16 to claim 28, wherein said drying composition is trimethyl orthoformiate as orthoester and ethyl trifluoroacetate as catalyst precursor.

30. Process according to any of claims 16 to claim 28, wherein said drying composition is trimethyl orthoformiate as orthoester and 4 weight-% ethyl trifluoroacetate as catalyst precursor.

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Application No: GB1703665.8 Examiner: Dr Leah Morris