Reivindicaciones
1. A compound having general formula (I) <img class="EMIRef" id="8658350-00520000" /> wherein X represents a spacer selected from: a) a xylylene radical non-substituted or optionally substituted with an R4O alcoxy group, wherein R4 is a linear or branched C6-C12 alkyl group, b) a C5-C7 alkylidene radical, c) a R5-O-R5 group, wherein R5 is a C2-C3 alkylidene radical, and d) a xanthene-derived group having formula (II) <img class="EMIRef" id="8658350-00530000" /> R1 is an H atom or a C1-C3 alkyl radical, R2 is an H atom or a linear or branched C1-C8 alkyl radical, and R3 is a linear or branched C4-C8 alkyl radical 2. A compound having general formula (I) according to claim 1 wherein X is a non-substituted xylylene radical, R1 is an H atom or a methyl radical, R2 is an H atom or an alkyl radical selected from methyl, butyl, isopentyl and octyl, and R3 is an alkyl radical selected from butyl, isopentyl and octyl. 3. A compound having general formula (I) according to claim 1 wherein X is a xylylene radical substituted with an R4O alcoxy group, wherein R4 is an alkyl radical selected from hexyl, sec-heptyl and dodecyl, R1 is an H atom, and R2=R3 is butyl. 4. A compound having general formula (I) according to claim 1 wherein X is a C5-C7 alkylidene radical, R1 is an H atom, and R2=R3 is an alkyl radical selected from butyl and octyl. 5. A compound having general formula (I) according to claim 1 wherein X is a R5-O-R5 group, wherein R5 is a C2-C3 alkylidene radical, R1 is an H atom, and R2=R3 is octyl. 6. A compound having general formula (I) according to claim 1 wherein X is a xanthene-derived group having formula (II), R1 is an H atom, and R2=R3 is butyl. 7. A compound having general formula (I) according to claim 1, selected from the following group: [1] 2-Butylcarbamoylmethoxy-N-[3-[(2-butylcarbamoylmethoxy-acetylamino)methyl]benzyl]acetamide, [2] 2-[(Butyl-methylcarbamoyl)methoxy]-N-[3-[(2-butyl-methylcarbamoyl)methoxyacetylamino]methyl]benzyl]acetamide, [3] 2-Dibutylcarbamoylmethoxy-N-[3-[(2-dibutylcarbamoyl-methoxy-acetylamino)methyl]benzyl]acetamide, [4] 2-Dioctylcarbamoylmethoxy-N-[3-[(2-dioctylcarbamoyl-methoxy-acetylamino)methyl]benzyl]acetamide, [5] 2-[(Methyloctylcarbamoyl)methoxy]-N-[3-[(2-[(methyloctyl-carbamoyl)methoxy]acetylamino]methyl]benzyl]acetamide, [6] 2-[[Bis(3-methylbutyl)carbamoyl]methoxy]-N-[3-[(2-[[bis-(3-methylbutyl)carbamoyl]methoxy]acetylamino)methyl]-benzyl]-acetamide, [7] N-Methyl-N-[3-[(methyl-[2-[(methyloctylcarbamoyl)methoxy]-acetyl]amino)methyl]benzyl]-2-[(methyloctylcarbamoyl)methoxy]-acetamide, [8] 2-[[4-([2-[Dioctylcarbamoyl)methoxy]acetylamino]methyl)-benzylcarbamoyl]methoxy]-N,N-dioctylacetamide, [9] 2-Di-butylcarbamoylmethoxy-N-[3-[(2-dibutylcarbamoyl-methoxyacetylamino)methyl]-5-hexyloxybenzyl]acetamide, [10] 2-Di-butylcarbamoylmethoxy-N-[3-[(2-dibutyl-carbamoyl-methoxyacetylamino)methyl]-5-(1-methylhexyloxy)benzyl]-acetamide, [11] 2-Di-butylcarbamoylmethoxy-N-[3-[(2-dibutyl-carbamoyl-methoxyacetylamino)methyl]-5-dodecyloxybenzyl]acetamide, [12] 2-Dibutylcarbamoylmethoxy-N-[5-(2-dibutylcarbamoyl-methoxyacetylamino)pentyl]acetamide, [13] 2-Dioctylcarbamoylmethoxy-N-[5-(2-dioctylcarbamoyl-methoxyacetylamino)pentyl]acetamide, [14] 2-Dibutylcarbamoylmethoxy-N-[6-(2-dibutylcarbamoyl-methoxyacetylamino)hexyl]acetamide, [15] 2-Dioctylcarbamoylmethoxy-N-[6-(2-dioctylcarbamoyl-methoxyacetylamino)hexyl]acetamide, [16] 2-Dioctylcarbamoylmethoxy-N-[7-(2-dioctylcarbamoyl-methoxyacetylamino)heptyl]acetamide, [17] 2-Dioctylcarbamoylmethoxy-N-[2-[2-(2-dioctylcarbamoyl-methoxyacetylamino)ethoxy]ethyl]acetamide, [18] 2-Dioctylcarbamoylmethoxy-N-[3-[3-(2-dioctylcarbamoyl-methoxyacetylamino)propoxy]propyl]acetamide, and [19] 2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4,5-dicarboxylic acid bis-[[3-(2-dibutylcarbamoylmethoxy-acetylamino)propyl]amide]. 8. A process for obtaining a compound having general formula (I) wherein X is a non-substituted xylylene radical, comprising reacting a compound having formula (III), <img class="EMIRef" id="8658350-00540000" /> with a compound having formula (IV) <img class="EMIRef" id="8658350-00550000" /> in an inert solvent and in the presence of an activating agent, R1, R2 and R3 having the meaning mentioned in claim 1. 9. A process for obtaining a compound having general formula (I) wherein X is a xylylene radical substituted with an R4O alcoxy group, comprising reacting a compound having formula (VIII), <img class="EMIRef" id="8658350-00560000" /> with a compound having formula (IV) in an inert solvent and in the presence of an activating agent, followed by a hydrogenation reaction, in an inert solvent and in the presence of a hydrogenation catalyst, giving rise to a compound having formula (IX), <img class="EMIRef" id="8658350-00570000" /> followed by an O-alkylation reaction with BrR4, in an inert solvent and in the presence of a base, R1, R2, R3 and R4 having the meaning mentioned in claim 1. 10. A process according to claim 9, wherein the compound having formula (VIII) is obtained by the O-benzylation with BrBn of a compound having formula (V), <img class="EMIRef" id="8658350-00580000" /> in an inert solvent and in the presence of a base, followed by a reduction reaction with LiAlH4 in an inert solvent, and by the reaction of the formed dialcohol having formula (VI) <img class="EMIRef" id="8658350-00590000" /> with SOCl2, giving rise to a compound having formula (VII) <img class="EMIRef" id="8658350-00600000" /> which is subjected to a Gabriel synthesis reaction with potassium phthalimide, in an inert solvent and in the presence of sodium iodide, followed by treatment with hydrazine in an inert solvent, to obtain the compound having formula (VIII) 11. A process for obtaining a compound having general formula (I) wherein X is a C5-C7 alkylidene radical, comprising reacting a compound having formula (X) HNR1-(CH2)n- NHR1 (X) with a compound having formula (IV) in an inert solvent and in the presence of an activating agent, R1, R2 and R3 having the meaning mentioned in claim 1 and wherein n is 5, 6 or 7. 12. A process for obtaining a compound having general formula (I) wherein X is a R5-O-R5 group, wherein R5 is a C2-C3 alkylidene group, comprising reacting a compound having formula (XI) HNR1-(CH2)n -O -(CH2)n NHR1 (XI) with a compound having formula (IV), in an inert solvent and in the presence of an activating agent, R1, R2 and R3 having the meaning mentioned in claim 1 and wherein n is 2 or 3. 13. A process for obtaining a compound having general formula (I) wherein X is a xanthene-derived group having formula (II), comprising reacting a compound having formula (XIV) <img class="EMIRef" id="8658350-00610000" /> with a compound having formula (IV), in an inert solvent and in the presence of an activating agent, R1, R2 and R3 having the meaning mentioned in claim 1. 14. A process according to claim 13, wherein the compound having formula (XIV) is obtained by reacting a compound having formula (XII) <img class="EMIRef" id="8658350-00620000" /> with a compound having formula (XIII) <img class="EMIRef" id="8658350-00630000" /> R1 having the meaning mentioned in claim 1, in an inert solvent and in the presence of an activating agent and of a base, followed by treatment with acid. 15. The use of a compound having general formula (I), according to any one of claims 1-7, for the extraction of lanthanides [Ln(III)] and actinides [An(III)] present in aqueous nitric solutions. 16. The use according to claim 15, for the extraction of lanthanides [Ln(III)] and actinides [An(III)] present in high-level radioactive liquid wastes. 17. A method for the extraction of lanthanides [Ln(III)] and actinides [An(III)] from an aqueous nitric solution comprising: a) contacting the aqueous nitric solution containing lanthanides [Ln(III)] and actinides [An(III)] with an organic solution comprising an extractant having general formula (I) and an organic solvent, and b) extracting the actinides [An(III)] and the lanthanides [Ln(III)] from the acid solution, after a contact time period. 18. A method according to claim 17, characterized in that the contact time period in step b) is 1 to 5 minutes. 19. A method according to claim 17, characterized in that the organic solvent of the organic solution is selected from tetrachloroethane, n-heptane, 1-octanol, TPH, n-dodecane and mixtures thereof. 20. A method according to claim 19, characterized in that the solvent of the organic solution is selected from a mixture of TPH and 5-10% (v/v) of 1-octanol and a mixture of n-dodecane and 5-10% (v/v) of 1-octanol. 21. A method according to claim 20, characterized in that the solvent of the organic solution is a mixture of TPH and 5% (v/v) of 1-octanol. 22. An extracting solution for the extraction of, lanthanides [Ln(III)] and actinides [An(III)] from aqueous nitric solutions and preferably from high-level radioactive liquid wastes, comprising an extractant having general formula (I) and a solvent selected from tetrachloroethane, n-heptane, 1-octanol, TPH, n-dodecane and mixtures thereof. 23. An extracting solution according to claim 22, characterized in that the solvent is selected from a mixture of TPH and 5-10% (v/v) of 1-octanol and a mixture of n-dodecane and 5-10% (v/v) of 1-octanol. 24. An extracting solution according to claim 23, characterized in that the solvent is a mixture of TPH and 5% (v/v) of 1-octanol.
