CH636611A5 - PROCEDURE FOR THE PREPARATION OF REPLACED DIHYDROPHURANS. - Google Patents
PROCEDURE FOR THE PREPARATION OF REPLACED DIHYDROPHURANS. Download PDFInfo
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- CH636611A5 CH636611A5 CH1083578A CH1083578A CH636611A5 CH 636611 A5 CH636611 A5 CH 636611A5 CH 1083578 A CH1083578 A CH 1083578A CH 1083578 A CH1083578 A CH 1083578A CH 636611 A5 CH636611 A5 CH 636611A5
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- Prior art keywords
- formula
- preparation
- reaction
- methyl
- procedure
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Links
- 238000000034 method Methods 0.000 title claims description 12
- 238000002360 preparation method Methods 0.000 title claims description 7
- 238000007363 ring formation reaction Methods 0.000 claims description 5
- QUPDWYMUPZLYJZ-UHFFFAOYSA-N ethyl Chemical group C[CH2] QUPDWYMUPZLYJZ-UHFFFAOYSA-N 0.000 claims description 4
- -1 methyl radicals Chemical class 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 150000001875 compounds Chemical class 0.000 claims description 3
- 125000004852 dihydrofuranyl group Chemical group O1C(CC=C1)* 0.000 claims description 3
- 239000012298 atmosphere Substances 0.000 claims description 2
- 229910052799 carbon Inorganic materials 0.000 claims description 2
- 239000003729 cation exchange resin Substances 0.000 claims description 2
- WCYWZMWISLQXQU-UHFFFAOYSA-N methyl Chemical compound [CH3] WCYWZMWISLQXQU-UHFFFAOYSA-N 0.000 claims description 2
- 239000012429 reaction media Substances 0.000 claims description 2
- 239000003054 catalyst Substances 0.000 claims 1
- 229940023913 cation exchange resins Drugs 0.000 claims 1
- 150000003254 radicals Chemical class 0.000 claims 1
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- VZGDMQKNWNREIO-UHFFFAOYSA-N tetrachloromethane Chemical compound ClC(Cl)(Cl)Cl VZGDMQKNWNREIO-UHFFFAOYSA-N 0.000 description 6
- 239000000203 mixture Substances 0.000 description 5
- 239000000047 product Substances 0.000 description 5
- 229920005989 resin Polymers 0.000 description 5
- 239000011347 resin Substances 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- INAXVXBDKKUCGI-UHFFFAOYSA-N 4-hydroxy-2,5-dimethylfuran-3-one Chemical compound CC1OC(C)=C(O)C1=O INAXVXBDKKUCGI-UHFFFAOYSA-N 0.000 description 4
- 238000001914 filtration Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 229920001429 chelating resin Polymers 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000008020 evaporation Effects 0.000 description 2
- 238000000605 extraction Methods 0.000 description 2
- 150000002240 furans Chemical class 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- CBFCDTFDPHXCNY-UHFFFAOYSA-N icosane Chemical compound CCCCCCCCCCCCCCCCCCCC CBFCDTFDPHXCNY-UHFFFAOYSA-N 0.000 description 2
- 238000002955 isolation Methods 0.000 description 2
- 239000012299 nitrogen atmosphere Substances 0.000 description 2
- 239000002304 perfume Substances 0.000 description 2
- 238000000746 purification Methods 0.000 description 2
- 239000011541 reaction mixture Substances 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 1
- RYHBNJHYFVUHQT-UHFFFAOYSA-N 1,4-Dioxane Chemical compound C1COCCO1 RYHBNJHYFVUHQT-UHFFFAOYSA-N 0.000 description 1
- OGWRZRITEAGNCV-UHFFFAOYSA-N 2,5-dihydroxyheptane-3,4-dione Chemical compound CCC(O)C(=O)C(=O)C(C)O OGWRZRITEAGNCV-UHFFFAOYSA-N 0.000 description 1
- MLOYTUCDJQWVSY-UHFFFAOYSA-N 2,5-dihydroxyhexane-3,4-dione Chemical compound CC(O)C(=O)C(=O)C(C)O MLOYTUCDJQWVSY-UHFFFAOYSA-N 0.000 description 1
- GWCRPYGYVRXVLI-UHFFFAOYSA-N 2-ethyl-4-hydroxy-5-methyl-3(2H)-furanone Chemical compound CCC1OC(C)=C(O)C1=O GWCRPYGYVRXVLI-UHFFFAOYSA-N 0.000 description 1
- VJMSGSIUSDPZPA-UHFFFAOYSA-N 2-ethyl-5-methylfuran-3-one Chemical compound CCC1OC(C)=CC1=O VJMSGSIUSDPZPA-UHFFFAOYSA-N 0.000 description 1
- SKJNEYSTLJSDDX-UHFFFAOYSA-N 5-ethyl-2-methylfuran-3-one Chemical compound CCC1=CC(=O)C(C)O1 SKJNEYSTLJSDDX-UHFFFAOYSA-N 0.000 description 1
- QJYOEDXNPLUUAR-UHFFFAOYSA-N 5-ethyl-4-hydroxy-2-methylfuran-3-one Chemical compound CCC1=C(O)C(=O)C(C)O1 QJYOEDXNPLUUAR-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000008346 aqueous phase Substances 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 239000001307 helium Substances 0.000 description 1
- 229910052734 helium Inorganic materials 0.000 description 1
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 1
- KXUSQYGLNZFMTE-UHFFFAOYSA-N hex-2-yne-1,1-diol Chemical compound CCCC#CC(O)O KXUSQYGLNZFMTE-UHFFFAOYSA-N 0.000 description 1
- 229910052500 inorganic mineral Inorganic materials 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000001819 mass spectrum Methods 0.000 description 1
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 description 1
- 239000011707 mineral Substances 0.000 description 1
- 150000007522 mineralic acids Chemical class 0.000 description 1
- VAMFXQBUQXONLZ-UHFFFAOYSA-N n-alpha-eicosene Natural products CCCCCCCCCCCCCCCCCCC=C VAMFXQBUQXONLZ-UHFFFAOYSA-N 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 150000007524 organic acids Chemical class 0.000 description 1
- 235000005985 organic acids Nutrition 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000000859 sublimation Methods 0.000 description 1
- 230000008022 sublimation Effects 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
- C07D307/02—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings
- C07D307/34—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members
- C07D307/56—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having two or three double bonds between ring members or between ring members and non-ring members with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
- C07D307/60—Two oxygen atoms, e.g. succinic anhydride
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Fats And Perfumes (AREA)
- Seasonings (AREA)
- Furan Compounds (AREA)
- Cosmetics (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Heterocyclic Carbon Compounds Containing A Hetero Ring Having Oxygen Or Sulfur (AREA)
Description
La presente invenzione si riferisce ad un nuovo procedimento per la preparazione di diidrofurani sostituiti di formula (I) The present invention relates to a new process for the preparation of substituted dihydrofurans of formula (I)
HO I HAVE
cioè di 2,5-dialchil-4-idrossi-2,3-diidrofuran-3-oni, in cui i due R sono radicali metilici o in cui uno degli R è un radicale metilico e l'altro è un radicale etilico a partire da composti di formula i.e. 2,5-dialkyl-4-hydroxy-2,3-dihydrofuran-3-oni, in which the two R are methyl radicals or in which one of the R is a methyl radical and the other is a starting ethyl radical from compounds of formula
CH, CH-CO-CO-CH-R CH, CH-CO-CO-CH-R
I I <«> I I <«>
OH OH OH OH
in cui R rappresenta un radicale metilico o etilico. wherein R represents a methyl or ethyl radical.
Il procedimento per la preparazione di detti diidrofurani sostituiti di formula (I) è caratterizzato nella rivendicazione 1 precedente. The process for preparing said substituted dihydrofurans of formula (I) is characterized in claim 1 above.
I prodotti di formula I possiedono valide proprietà organolettiche per cui presentano un notevole interesse per l'industria alimentare, farmaceutica e dei profumi. Formula I products possess valid organoleptic properties and are therefore of considerable interest to the food, pharmaceutical and perfume industries.
I prodotti di formula II sono ottenibili con metodi economici noti (vedi per es. L. Re e G. Ohloff, US Patent 3 576 014 della Lirmenich & Cie.; L. Re e V. Caciagli, Ger. Offen, n. 2 426 051 della Snamprogetti S.p.A.). The products of formula II are obtainable with known economic methods (see for example L. Re and G. Ohloff, US Patent 3 576 014 of Lirmenich & Cie .; L. Re and V. Caciagli, Ger. Offen, n. 2 426 051 of Snamprogetti SpA).
Precedentemente il metodo migliore per ottenere i composti di formula I era basato sulla ciclizzazione dei precursori di formula II tramite acidi minerali od organici, o tamponi acidi, solubili nel mezzo di reazione. Previously the best method for obtaining the compounds of formula I was based on the cyclization of the precursors of formula II by means of mineral or organic acids, or acidic buffers, soluble in the reaction medium.
Il metodo oggetto della presente invenzione offre i seguenti vantaggi rispetto al metodo precedente: The method object of the present invention offers the following advantages compared to the previous method:
(1) L'agente di ciclizzazione, che deve essere usato in forte quantità rispetto al dìoldione con ambedue i metodi, può essere recuperato per semplice filtrazione e riutilizzato. (1) The cyclization agent, which must be used in large quantities with respect to the dioneion with both methods, can be recovered by simple filtration and reused.
(2) L'isolamento del derivato furanico dalla miscela di reazione è operativamente più semplice, in quanto non comporta l'estrazione in continuo del prodotto dalla fase acquosa con etere etilico (come nel metodo precedente) e può essere effettuato per semplice evaporazione, dopo filtrazione dalla resina, del filtrato acquoso, seguita da estrazione del prodotto dal residuo con un solvente opportuno (preferibilmente tetracloruro di carbonio) e da evaporazione di detto solvente. (2) The isolation of the furan derivative from the reaction mixture is operationally simpler, as it does not involve the continuous extraction of the product from the aqueous phase with ethyl ether (as in the previous method) and can be carried out by simple evaporation, after filtration from the resin of the aqueous filtrate, followed by extraction of the product from the residue with a suitable solvent (preferably carbon tetrachloride) and evaporation of said solvent.
(3) I derivati furanici isolati dalla miscela di reazione non richiedono ulteriore purificazione (purezza: 95%), mentre, per la preparazione secondo il metodo precedente del derivato I in cui i due R sono radicali metilici, una purificazione per sublimazione deve essere fatta seguire all'isolamento del grezzo di reazione. (3) The furan derivatives isolated from the reaction mixture do not require further purification (purity: 95%), while, for the preparation according to the previous method of the derivative I in which the two R are methyl radicals, a sublimation purification must be done follow the isolation of the reaction raw product.
Più precisamente, per la preparazione dei derivati di formula I, il dioldione di partenza di formula II viene fatto reagire in una miscela di acqua con un solvente idrofilo (quale metanolo, etanolo, diossano, ecc.) o, preferibilmente, in acqua pura con un resina a scambio cationico (quale Am-berlite IR 122, IR 124, IR 112, IR 200 o IR 120, preferibilmente con quest'ultima) ad una temperatura compresa fra 50 e 150°C (preferibilmente a 100°C ed in una atmosfera inerte (per es. azoto). More precisely, for the preparation of the derivatives of formula I, the starting dioldione of formula II is reacted in a mixture of water with a hydrophilic solvent (such as methanol, ethanol, dioxane, etc.) or, preferably, in pure water with a cation exchange resin (such as Am-berlite IR 122, IR 124, IR 112, IR 200 or IR 120, preferably with the latter) at a temperature between 50 and 150 ° C (preferably at 100 ° C and in a inert atmosphere (e.g. nitrogen).
Nel caso del dioldione di formula II in cui R rappresenta un radicale etilico, la ciclizzazione fornisce una miscela dei due isomeri 2-etil-5-metil-2,3-diidrofuran-3-one e 5-etil--2-metil-2,3-diidrofuran-3-one, in un rapporto di ca. 2:1, che può essere usata come tale nell'industria alimentare, farmaceutica e dei profumi. In the case of the dioldione of formula II wherein R represents an ethyl radical, the cyclization provides a mixture of the two isomers 2-ethyl-5-methyl-2,3-dihydrofuran-3-one and 5-ethyl - 2-methyl- 2,3-dihydrofuran-3-one, in a ratio of approx. 2: 1, which can be used as such in the food, pharmaceutical and perfume industries.
Le particolarità operative saranno comunque più evidenti dall'esame dei seguenti esempi: The operational particularities will however be more evident from the examination of the following examples:
Esempio 1 Example 1
Preparazione 2,5-dimetil-4-idrossi-2,3-diidrofuran-3-one Preparation 2,5-dimethyl-4-hydroxy-2,3-dihydrofuran-3-one
A 1,040 g di 2,5-diidrossiesan-3,4-dione grezzo sciolti in 20 cc di acqua vengono aggiunti 4,75 g di resina Amberlite IR 120 e la miscela scaldata a riflusso sotto agitazione in atmosfera di azoto per 4 ore. La soluzione acquosa, dopo filtrazione della resina, si neutralizza con NaOH 2N e si porta a secco sotto vuoto a temperatura ambiente. To 1,040 g of crude 2,5-dihydroxyhexan-3,4-dione dissolved in 20 cc of water, 4.75 g of Amberlite IR 120 resin are added and the mixture heated under reflux under stirring in a nitrogen atmosphere for 4 hours. After filtering the resin, the aqueous solution is neutralized with NaOH 2N and dried under vacuum at room temperature.
Il residuo oleoso che si ottiene si estrae con tre porzioni successive di 10 mi di tetracloruro di carbonio. Dopo allontanamento del solvente sotto vuoto a temperatura ambiente si ottiene un residuo di 0,327 g (resa, 32% dall'esin-diolo) di 2,5-dimetil-4-idrossi-2,3-diidrofuran-3-one oleoso che cristallizza spontaneamente, di purezza gas-cromatografica del 95 % (le analisi g.c. sono state eseguite con uno strumento Hewlett-Packard Modello 7620-A munito di detector a termoconducibilità. Colonna 6 ft X 1/g in., di 4% SE 30 su Chromosorb G silanizzato (60-80 mesh); 170°C per 6', poi 170) 230°C (30°C/min) con 8 ml/min di elio, usando n-eicosano come standard interno), p.f. 60-70°C, spettri i.r., di massa ed nmr in accordo con la letteratura (J.O. R.odm et al. J. Food Science, 30, 280 [1965]). The oily residue obtained is extracted with three successive portions of 10 ml of carbon tetrachloride. After removal of the solvent under vacuum at room temperature, a residue of 0.327 g (yield, 32% from hexin-diol) of 2,5-dimethyl-4-hydroxy-2,3-dihydrofuran-3-one oily is obtained which crystallizes spontaneously, gas chromatographic purity of 95% (gc analyzes were performed with a Hewlett-Packard Model 7620-A instrument equipped with a heat-conducting detector. Column 6 ft X 1 / g in., of 4% SE 30 on Chromosorb G silanized (60-80 mesh); 170 ° C for 6 ', then 170) 230 ° C (30 ° C / min) with 8 ml / min of helium, using n-eicosane as internal standard), mp 60-70 ° C, mass and nmr spectra according to literature (J.O. R.odm et al. J. Food Science, 30, 280 [1965]).
Esempio 2 Example 2
Preparazione di 2-etil-5-metil-4-idrossi-2,3-diìdrofuran-3--one e 5-etil-2-metil-4-idrossi-2,3-diidrofuran-3-one Preparation of 2-ethyl-5-methyl-4-hydroxy-2,3-dihydrofuran-3 - one and 5-ethyl-2-methyl-4-hydroxy-2,3-dihydrofuran-3-one
A 1,139 g di 2,5-diidrossieptan-3,4-dione grezzo (preparato da 3-eptin-2,5-diolo), sciolti in 20 cc di acqua ven5 At 1,139 g of crude 2,5-dihydroxyheptan-3,4-dione (prepared from 3-heptin-2,5-diol), dissolved in 20 cc of ven5 water
io I
15 15
20 20
25 25
30 30
35 35
40 40
45 45
50 50
55 55
60 60
65 65
3 3
636611 636611
gono aggiunti 4,75 g di resina Amberlite IR 120 e la miscela scaldata a riflusso in atmosfera di azoto per 6 ore. La soluzione acquosa, dopo filtrazione della resina, si neutralizza con NaOH 2N e si porta a secco sotto vuoto a temperatura ambiente. Il residuo oleoso che si ottiene si estrae con tre porzioni successive di 10 mi di tetracloruro di carbonio. Dopo allontanamento del solvente sotto vuoto a temperatura ambiente si ottiene un residuo oleoso di 0,325 g 4.75 g of Amberlite IR 120 resin are added and the mixture is heated under reflux in a nitrogen atmosphere for 6 hours. After filtering the resin, the aqueous solution is neutralized with NaOH 2N and dried under vacuum at room temperature. The oily residue obtained is extracted with three successive portions of 10 ml of carbon tetrachloride. After removal of the solvent under vacuum at room temperature, an oily residue of 0.325 g is obtained
(resa, 29% dall'eptindiolo), costituito da una miscela di 2-etil-5-metiI-4-idrossi-2,3-diidrofuran-3-one- e 5-etil-2-me-til-4-idrossi-2,3-diidrofuran-3-one (—2:1), di purezza gas--cromatografica del 94% (condizioni g.c. come per il 2-5-5 -dimetil-4-idrossi-2,3-diidrofuran-3-one), p.e. 62-65°C/0,015 mm'Hg, spettri di massa ed nmr in accordo con la letteratura. (yield, 29% from heptindiol), consisting of a mixture of 2-ethyl-5-methyl-4-hydroxy-2,3-dihydrofuran-3-one- and 5-ethyl-2-me-tyl-4- hydroxy-2,3-dihydrofuran-3-one (—2: 1), gas chromatographic purity of 94% (gc conditions as for 2-5-5-dimethyl-4-hydroxy-2,3-dihydrofuran -3-one), eg 62-65 ° C / 0.015 mm'Hg, mass spectra and nmr according to the literature.
v v
Claims (3)
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| IT2880077A IT1087026B (en) | 1977-10-20 | 1977-10-20 | PROCEDURE FOR THE PREPARATION OF 2,5-DIALKYL-4-HYDROXY-2,3-DIIDROFURAN-3-ONI |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CH636611A5 true CH636611A5 (en) | 1983-06-15 |
Family
ID=11224207
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CH1083578A CH636611A5 (en) | 1977-10-20 | 1978-10-19 | PROCEDURE FOR THE PREPARATION OF REPLACED DIHYDROPHURANS. |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS5463068A (en) |
| BE (1) | BE871421A (en) |
| CA (1) | CA1110255A (en) |
| CH (1) | CH636611A5 (en) |
| DE (1) | DE2845843C3 (en) |
| FR (1) | FR2406636A1 (en) |
| GB (1) | GB2006205B (en) |
| IT (1) | IT1087026B (en) |
| LU (1) | LU80371A1 (en) |
| NL (1) | NL7810532A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2831676A1 (en) * | 1978-07-19 | 1980-02-07 | Basf Ag | NEW BIS-EPOXY-DIALKOXY ALKANES, THEIR PRODUCTION AND USE |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1383492A (en) * | 1970-12-21 | 1974-02-12 | Unilever Ltd | Dicarbonyl compounds and preparation of dihydrofuranones therefrom |
-
1977
- 1977-10-20 IT IT2880077A patent/IT1087026B/en active
-
1978
- 1978-09-29 CA CA312,375A patent/CA1110255A/en not_active Expired
- 1978-10-11 GB GB7840115A patent/GB2006205B/en not_active Expired
- 1978-10-16 LU LU80371A patent/LU80371A1/en unknown
- 1978-10-17 FR FR7829553A patent/FR2406636A1/en active Granted
- 1978-10-18 JP JP12745678A patent/JPS5463068A/en active Pending
- 1978-10-19 CH CH1083578A patent/CH636611A5/en not_active IP Right Cessation
- 1978-10-20 DE DE19782845843 patent/DE2845843C3/en not_active Expired
- 1978-10-20 BE BE191250A patent/BE871421A/en not_active IP Right Cessation
- 1978-10-20 NL NL7810532A patent/NL7810532A/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| DE2845843C3 (en) | 1980-12-18 |
| JPS5463068A (en) | 1979-05-21 |
| FR2406636B1 (en) | 1981-08-14 |
| DE2845843A1 (en) | 1979-04-26 |
| BE871421A (en) | 1979-04-20 |
| IT1087026B (en) | 1985-05-31 |
| DE2845843B2 (en) | 1980-04-30 |
| LU80371A1 (en) | 1979-03-19 |
| CA1110255A (en) | 1981-10-06 |
| FR2406636A1 (en) | 1979-05-18 |
| GB2006205B (en) | 1982-03-31 |
| NL7810532A (en) | 1979-04-24 |
| GB2006205A (en) | 1979-05-02 |
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