Assembly comprising a container (50, 51) of the type having a tubular shape comprising a head surface at the upper end of the container (50, 51) from which a substantially cylindrical neck projects, wherein said tubular shape comprises a longitudinally extending surface which intersects said head surface, the intersection of said longitudinally extending surface with said head surface delimiting said upper end of the container (50, 51), a closing device (1, 71, 91, 101) associated with said container (50, 51), said closing device comprising: a main body (2, 72, 92) connected to said container (50, 51) and comprising an opening for the passage of a product flowing out of said container (50, 51), a cover (12, 82) comprising means for closing said opening and suited to be arranged in a closed position with respect to said main body (2, 72, 92), in which said closing means intercept said opening, and suited to be arranged in an open position, in which said closing means do not intercept said opening, wherein said main body (2, 72, 92) and said cover (12, 82) are integral with each other, characterized in that in said closed position at least one portion of said cover (12, 82) does not face said main body (2, 72, 72) but faces directly the portion of said head surface external to said substantially cylindrical neck when said closing device (1, 71, 91, 101) is connected to said container (50, 51), where a lower portion of said main body (2, 72, 92), said lower portion facing the container (50, 51), comprises two projecting cylindrical portions (7, 8) defining a substantially annular area suited to accommodate said substantially cylindrical neck of said container (50, 51) and at the level of one of the external cylindrical portions (7, 8) there are two projecting edges (9a, 9b) suited to be snapped in corresponding seats obtained in the substantially cylindrical neck of said container (50, 51) in order to realize the connection between said main body (2, 72, 92) of said closing device (1, 71, 91, 101) and said container (50, 51), and in that said cover (12, 82) has at its periphery a side surface bearing, in said closed position, against said upper end of said container. a main body (2, 72, 92) connected to said container (50, 51) and comprising an opening for the passage of a product flowing out of said container (50, 51), a cover (12, 82) comprising means for closing said opening and suited to be arranged in a closed position with respect to said main body (2, 72, 92), in which said closing means intercept said opening, and suited to be arranged in an open position, in which said closing means do not intercept said opening, wherein said main body (2, 72, 92) and said cover (12, 82) are integral with each other, characterized in that in said closed position at least one portion of said cover (12, 82) does not face said main body (2, 72, 72) but faces directly the portion of said head surface external to said substantially cylindrical neck when said closing device (1, 71, 91, 101) is connected to said container (50, 51), where a lower portion of said main body (2, 72, 92), said lower portion facing the container (50, 51), comprises two projecting cylindrical portions (7, 8) defining a substantially annular area suited to accommodate said substantially cylindrical neck of said container (50, 51) and at the level of one of the external cylindrical portions (7, 8) there are two projecting edges (9a, 9b) suited to be snapped in corresponding seats obtained in the substantially cylindrical neck of said container (50, 51) in order to realize the connection between said main body (2, 72, 92) of said closing device (1, 71, 91, 101) and said container (50, 51), and in that said cover (12, 82) has at its periphery a side surface bearing, in said closed position, against said upper end of said container.