The invention relates to a series of new compounds of the general formula I:     in which R4 and X are as defined above and the -COOE group is an   or an ester thereof, in which R3, R4 and X are as defined before and -COY is a reactive derivative of a carboxylic group, preferably a lower alkyl ester group, with an amine R1R2NH in which R1 and R2 are as defined above. The starting materials of formula II are new compounds. In one method for the preparation of these new compounds 4chloroisophthalic acid is used as starting material. By nitration of this compound a nitro group is introduced in the 5-position. After esterification of the two free carboxylic acid groups and treatment with R4-X-H, in which R4 and X are as defined, the R4X radical replaces the chlorine atom in the 4-position, forming an alkyl 4-R4X-5-nitroisophthalate. The R4X radical can in the same manner be introduced in the corresponding free acids as well, whereafter an esterification is performed, if desired. Thereafter the nitro group is reduced into an amino group in known manner to yield an alkyl 4-R4X-5-aminoisophthalate. A catalytic reduction for instance with palladium-on-carbon as catalyst under slightly alkaline conditions, or ferrosulfate in ammonium hydroxide can be mentioned as suitable reducing agents, but other known methods can be used as well. In the case where the free isophthalic acid derivatives are obtained, these are transformed to the desired corresponding di-esters in known manner. By a partial saponification process by means of for instance the calculated amount of alkali hydroxide in ethanol the ester is partly saponified to a 4-R4X-3-amino-5-carbalkoxybenzoic acid of the formula IV:     in which X is selected from the group consisting of -O-, -S-, and -NH-; R1 is selected from the group consisting of hydrogen and aliphatic radicals with from one to four carbon atoms; R2 is selected from the group consisting of hydrogen, saturated and unsaturated, straight and branched aliphatic radicals with from one to six carbon atoms, and aryl- and heterocyclic-substituted aliphatic radicals with from one to four carbon atoms; R3 is selected from the group consisting of saturated and unsaturated, straight and branched aliphatic radicals with from one to six carbon atoms, and aryl- and heterocyclic-substituted aliphatic radicals with from one to four carbon atoms, and R4 is selected from the group consisting of unsubstituted and substituted phenyl radicals. In particular, a straight or branched, saturated or unsaturated, aliphatic radical means e.g., a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, or tert. butyl radical, or one of the different isomeric pentyl or hexyl radicals, an alkenyl or alkynyl radical, e.g., a vinyl, allyl or propargyl radical. In the aromatically or heterocyclically substituted aliphatic radicals, the aromatic part of the radical can be a mono- or bicyclic aryl radical, e.g., a phenyl or naphthyl radical, the heterocyclic part of the radical can be a mono- or bicyclic radical containing one or more oxygen, sulphur and nitrogen atoms as ring members, e.g., 2-, 3or 4-pyridyl, 2- or 3-furyl or -thienyl, thiazolyl, imidazolyl, benzimidazolyl, and the corresponding hydrogenated ringsystems, and the aliphatic part of the radicals can contain 1 to 4 carbon atoms. Illustrative examples of such aromatically or heterocyclically substituted aliphatic radicals are benzyl, 1- Or 2-phenethyl, 1- or 2-naphthylmethyl, furylmethyl and the corresponding ethyl, propyl and butyl radicals. The salts of the compounds are pharmaceutically acceptable salts, such as alkali metal salts, alkaline earth metal salts, the ammonium salt or organic amine salts, e.g., mono-, di-, or trialkylamine salts, mono-, di-, or trialkanolamine salts, or cyclic amine salts. The esters of the compounds of formula I are particularly esters with lower alkanols, e.g., methanol or ethanol the different isomers of propanols and butanols, and substituted alkanols, e.g., cyanomethanol, or aryl-lower alkanols, e.g., benzylalcohol or phenylethanol. The above mentioned radicals R1 to R4 can be further substituted with hydroxy, alkyl, or alkoxy groups with from one to four carbon atoms, with halogen atoms, preferably fluorine, chlorine or bromine, or haloalkyl groups, e.g., a trifluoromethyl group. Whenever the expression ''''lower'''' is used in the present specification it stands for a radical containing from one to six carbon atoms. Many sulfamylbenzoic acid derivatives are known to possess diuretic activity. It has hitherto been generally held that the diuretic and saluretic activities of these benzoic acid derivatives are closely related to the presence of at least one sulfonamide group. It is therefore very surprising that the 5aminoisophthalic acid derivatives of the present invention have pronounced diuretic and saluretic activity with rapid onset of effect and high electrolyte excretion level. In experiments on dogs it has been shown that the present compounds are effective in doses less than 1 mg/kg, which means that they are at least as effective as the well-known diuretic furosemide, even if no sulfonamide group is present. The absence of the sulfonamide group and the particular structure of the compounds make them interesting also because allergic manifestations caused by prolonged use of the well known sulphonamide containing diuretics may be avoided by using the new compounds of the invention. This in connection with a very low toxicity makes the compounds of the present invention especially valuable from a therapeutic point of view in the treatment of different kinds of oedematous and hypertensive conditions where it is desirous to relieve excessive water and salt retension, e.g., in connection with heart and kidney diseases. The present compounds are effective after oral, enteral or parenteral administration, and are preferably prescribed in the form of tablets, pills, dragees, or capsules containing the free acid or salts thereof with atoxic bases, or the esters or amides thereof, mixed with carriers and/or auxiliary agents. Pharmaceutical organic or inorganic, solid or liquid carriers suitable for oral, enteral or parenteral administration can be used to make up compositions containing the present compounds. Gelatine, lactose, starch, magnesium stearate, talc, vegetable and animal fats and oils, gum, polyalkylene glycol, or other known carriers for medicaments are all suitable as carriers. The compositions may further contain other therapeutic compounds applied in the treatment of, for example oedemas and hypertension, besides the well known auxiliary agents. Such other compounds may be, for instance, Veratrumor Rauwolfia alkaloids, e.g., reserpine, rescinnamine or protoveratrine or synthetic hypotensive compounds, e.g., hydralazine, or other diuretics and saluretics, such as the well-known benzothiadiazines, e.g., hydroflumethiazide, bendroflumethiazide, and the like. Potassiumsparing diuretics, e.g., triamterene, may also be used in the preparation of the compositions. For some purposes it may be desirable to add small amounts of carboanhydrase inhibitors or aldosterone antagonists, e.g., spironolactone. Salts, which are soluble in water, may with advantage be administered by injection. The pharmaceutical preparations are useFul in the treatment of oedematous conditions, e.g., cardiac, hepatic, renal, lung and brain oedema, or oedematous conditions during pregnancy, and of pathological conditions which produce an abnormal retension of the electrolytes of the body, and in the treatment of hypertension. The parenteral preparations are in particular useful in the treatment of conditions in which a quick dehydration is desirable, e.g., in the intensive therapy in the case of oedemas in the lung. In the continuous therapy of patients suffering from e.g., hypertension, the tablets or capsules may be the appropriate form of pharmaceutical preparation owing to the prolonged effect obtained when the drug is given orally, in particular in the form of sustained-release tablets. In the treatment of heart failure and hypertension such tablets may advantageously contain other active components, as specified hereinbefore. The compounds of the invention can be prepared by various methods. In one embodiment a compound of formula II: or an ester thereof, in which X, R1, R2 and R4 are as defined above, is subjected to an alkylation process to form the compounds of formula I. This alkylation can be performed by a reaction with an alkylating agent of the formula R3-X'', in which R3 is as defined above and X'' stands for halogen, preferably chlorine or bromine, or a hydroxy group, a hydroxysulfonyloxy group, an R3oxysulfonyloxy group, or an alkyl- or arylsulfonyloxy group. The reaction can be performed in an alcoholic solvent in which case the corresponding ester of the compound of formula I can be formed simultaneously. If desired, the esters can be hydrolyzed to the corresponding free acids and vice versa in known manner. If desired, the R3 substituent can also be introduced by a wellknown reductive alkylation process by means of the appropriate aldehyde. In another embodiment the compounds of the invention can be prepared by treating a compound of formula III: in which X is selected from the group consisting of -O-, -S-, and -NH-; R1 is selected from the group consisting of hydrogen and aliphatic radicals with from one to four carbon atoms; R2 is selected from the group consisting of hydrogen, saturated and unsaturated, straight and branched aliphatic radicals with from one to six carbon atoms, and aryl- and heterocyclic-substituted aliphatic radicals with from one to four carbon atoms; R3 is selected from the group consisting of saturated and unsaturated, straight and branched aliphatic radicals with from one to six carbon atoms, and aryl- and heterocyclic-substituted aliphatic radicals with from one to four carbon atoms, and R4 is selected from the group consisting of unsubstituted and substituted phenyl radicals; to salts and esters of these compounds and to methods for their preparation. The present 5-aminoisophthalic acid derivatives have pronounced diuretic and saluretic activity with rapid onset of effect and high electrolyte excretion level. This invention relates to a series of new compounds, which are derived from 5-aminoisophthalic acid (3-amino-5-carboxybenzoic acid), to salts and esters of these compounds and to methods for the preparation of the new compounds. The compounds have the general formula I: